When you meet me on the internet, you are not entitled to know the legal identity that my local government recognizes me as. You get to see the screen name I am using to interact with you. If I choose to, I may have listed a face-to-face name I answer to. The name I share with you is the one I would like you to address me by. You do not win magic points by knowing the name that was on my birth certificate, or my current legal name. To pick a public and well-known example, insisting upon calling someone "William" when they have repeatedly stated that the name they answer to is "Ferrett" is really a dick move.
You can call someone anything you want to in the privacy of your own head, but when you are speaking to them, or speaking of them in a public forum, it is only basic courtesy to address them by their preferred name. If you address them by a name you know they do not like, you have failed basic politeness and should go back to kindergarten. If you act like a dick to me, you are not entitled to be treated like you are not being a dick.
You are not entitled to know whether I am someone you have met face-to-face. I am not entitled to know the same about you. It rather behooves both of us to be careful about sharing personal information with a stranger, either face-to-face or on the internet, but we don't have to admit it if we recognize each other.
You are not entitled to know whether I am biologically male, female, or something else. You are not entitled to know whether I think of myself as a man, a woman, both, a neuter, or something that mainstream society doesn't have the vocabulary to express. You are not entitled to know whether my self-expression matches the chromosomes I was born with. You are not entitled to know my legal sex, even if my workplace is. I may choose to share these things. I may choose to keep them private.
Sex is a very basic pigeonhole that we learn very young. We're taught that it matters, and file someone away into male or female when we meet them. Once it's taught, it can take enormous amounts of un-learning to stop doing it, or stop thinking that it matters. If we were to meet on the street, you would have a good guess about what sex I am. You would not look down my pants to prove to yourself that your guess was right. If you did, I would call for the cops and possibly punch you in the face. You do not necessarily have the same visual, audio, and kinesthetic information about me on the internet. You are not entitled to that on the internet. You are not entitled to that information in the world of written correspondence either. Fans of literature should look to George Eliot and James Tiptree, Jr.
If I do not note whether I am male, female, or other, I run the risk of having you assume incorrectly. This assumption usually says more about you than it does about me.
I may choose an image to associate with myself. That may or may not resemble what I actually look like. It may or may not be intended to represent me. Sometimes it's just a picture I like, not the mental image I'd like you to have when you think of the face that goes with the name.
You are not entitled to know my ethnic background. You are not entitled to know my nationality. You are not entitled to know what kind of upbringing I had. You are not entitled to know what my educational background is. You are not entitled to know my sexual orientation. You are not entitled to know what kind of clothes I wear. You are not entitled to know the color of my eyes, or the length, color, texture, presence, or absence of my hair. You are not entitled to know if I dye my hair, and if I do dye it, whether it's a color that is normally found on humans. You are not entitled to know if I shave parts of my body, especially not if the body parts are not ones you'd normally see. You are not entitled to know whether or not I am what you would consider attractive. You are not entitled to know if it's boxers or briefs. You are not entitled to know whether I have the normal number of limbs for a human being, or if I have any varyingly interesting or painful after-market additions or subtractions. You are not entitled to know whether I am a marathon runner in my spare time or if I am confined to bed because my body is disintegrating and I cannot even sit up.
Many of these things can be very helpful in knowing how to relate to someone. They are not necessary. On the internet, it is possible to not share certain basic stuff about yourself that is unavoidably shared when you meet someone face to face. Humans are used to using these things to cement a relationship, to build a model of the other person in one's head, to fill in the missing pieces, to relate to where the other party is coming from. It is untrue that no one on the internet cares about these things. Many people share these things. It is true that one can misrepresent these things. However, these things are not necessary to know, and you are not entitled to know them.
You may find that you have made assumptions. Have I ever said that I was male or female, or did you guess from my name? Did you pick up something from someone else talking about me? Are you sure that they were right? Did you assume that I was something because of the company I keep? Did you fill in my blanks based on people you have known before? You could be right. You could be wrong. You could be acting on prejudices and stereotypes. I cannot stop you from making assumptions. However, if you state your assumptions in public, and your assumptions are wrong, you may look like a dick. You may look like a dick even if your assumptions are right. You are certainly entitled to make yourself look like a dick in public, but you are not entitled to be treated like someone who is not acting like a dick when you are in fact acting like a dick. You are not entitled to me studying the entire history of your interactions with others before coming to the conclusion that you acted like a dick. You are not entitled to a clean slate once you have stopped acting like a dick this time.
You are not entitled to bombard me for making a public statement. You are not entitled to treat me as a toy for your entertainment. You are not entitled to use my time and energy for your profit. You are not entitled to my money unless we have agreed on a transaction involving a good or service from you, and then I am entitled to that good or service in return as agreed, and disputes about this are best handled in a court in a mutually agreeable jurisdiction. You are not entitled to my attention. You are not entitled to my feedback. You are not entitled to my consideration. I can dismiss you and your wants just as easily as you can dismiss me and mine. You are not entitled to the chance to change my mind. You are not entitled to read everything I feel like writing. You are not entitled to me expanding on all my thoughts if you didn't understand them the first time. You are not entitled to having a way to communicate with me. If I have made available a way to communicate with me, I am entitled to shut it down if I feel it is being abused. I am entitled to withdraw from communication in a recreational venue if the communication has become unproductive. You, too, are entitled to withdraw from communication.
You are not entitled to know all of the languages I speak. You may see my screen name without ever interacting with me. If I interact with you, you will probably learn at least one of the languages I can write in, unless of course I'm operating through translation of some sort. You can see my command of the language by the words I use to interact with you, assuming they're mine. You may never know whether I can pronounce the words I'm using, nor whether I'm stretching to words I don't ordinarily use, nor if I'm dumbing down my word choice to make sure you can understand what I mean. I may say I get it when I don't. I may understand you but ignore you.
You are not entitled to know the IP address I am connecting from unless I am connecting to a server you control. If we are interacting on a server you do not control, you are not entitled to know my IP address. You may try to gather it by including content from a server you control, such as images, but I am free to block them from being loaded by my browser. You are entitled to gather the IP address of anyone who comments in your space on LiveJournal. I am entitled to know whether you are gathering IP addresses. If I do not want my IP address gathered, I do not comment. If you do not want your IP address gathered in my journal, you do not comment.
You are also not entitled to know whether the IP address I am using right now is my regular IP address or not. Sometimes you can guess. Sometimes it is a matter of public record that this IP address is a proxy. Sometimes I have an IP that has been assigned to possibly thousands of residential customers in a large area belonging to a particular ISP. You may use various tricks and services to find out what journal that IP is likely to be associated with, but that is a rather specialist level of research, and not something you are entitled to know.
You are not entitled to know whether I am one person writing under one name, one person writing under many names, or a single name shared by a group. You are not entitled to know whether the person you knew under a certain fairly common nickname on one website is the same person using the same or a similar nickname, with a similar writing style, on another website. It's pretty much a certainty if they've the same e-mail address listed, if the sites both insist that you verify access to the e-mail address before having it listed, but it's not your right to know.
If I am using a sockpuppet for the purposes of acting like a dick, I do deserve to be found out and treated like one. If I am being a sufficient dick under one identity to be removed from a server for being a dick, then I deserve to have all of my accounts pulled. While it would be a public service for the owner of the server to identify the dick who was in command of those sockpuppets, you are not entitled to that information.
If I choose to withhold any of this information, it is information that I am entitled to withhold. You may have a social expectation for some of this information, but it is not your right to have it. If you make a big fuss about not having this information, why, exactly, are you spending time on the internet?
Is it useful to know these things? Yes. Very much so, in some cases. It is not required, and it is not your right. Speaking of some rights:
I am not entitled to publish damaging statements about you that are not true. That is called libel, and it is not legal.
I am not entitled to make credible threats to your safety and well-being. This is a scenario where the various internet-based services I am on should cooperate with your local law enforcement.
I am not entitled to reproduce your intellectual property without your permission. I am especially not entitled to profit from doing so.
I am permitted to hold and share opinions about you that are not flattering. Please see your local internets lawyer for the distinction between this and libel.
Shockingly, I may hold separate opinions of a body of work and the creator of that body of work. I may have no personal problem with you, but very deep issues with something you have written. (Whether that's actually a problem I have with you depends on how attached you are to that particular piece of writing. If it's an issue that's deep within your own self-image, then yeah, we may have problems.)
You are not entitled to me having a good opinion of you. That's okay. I'm not entitled to your having a good opinion of me either.
[Edited to add: now with a sequel: Privacy vs. Social Expectations, in particular to LiveJournal]