Ugh, this whole thread...see, this is why we can't have nice things.
My need to pass is coming from a number of different places; let me start by saying that in theory, gender bounderies mean nothing to me. They are something we've created as a society, and I believe that overall, they've done us a lot of harm. People can choose to do what they wish, and there's nothing wrong with being a masculine man or feminine woman, but that we mandate this behavior from people on the basis of gender is absolutely wrong. This is in theory.
The reality though is that sometimes, conforming is necessary. I have a number of goals in my life that have nothing to do with gender; those goals often conflict with my trans-ness. Firstly, I don't want to think about my gender at all times. I'm not planning on going stealth or anything, but it'd be nice to get to a point in my life where other people don't think about this so I won't have to. This is a huge emotional drain on me, and I can't really function when I'm worrying about how other people see me at all times. If other people know, I'm going to be forced to think about my gender, about how terribly wrong my body is, about everything else that just hasn't worked out so far in my transition. Passing would give me the opportunity to move on.
Another reason is that transphobia is very real, and I want the privilege that passing affords. Passing would make it easier for me to get jobs (and in my field, no job lasts longer than a few months). It would allow me a certain amount of security; that's really, really important. When you pass, you don't have to worry about being assaulted, or harassed, so long as nobody finds out. Being trans is not safe, and passibility helps allay the dangers we all face. I live in the New York metro area; it's not the most dangerous place in the world, but people do get harassed. They get beaten; a few even get killed. I don't feel the need to pass because I can't "love myself", or whatever else people here are going to say. I need to pass because if I can't, I will never be able to feel safe. That's a big deal in and of itself.
Even when I'm among people who aren't hostile, there are still problems that arise when everyone knows I'm trans. A big one is dating. I'm pansexual, but for the most part right now I'm interested in dating women. Dating lesbians; lesbians like other women. If I don't look like a woman, whatever that means, a lesbian won't be attracted to me. That's understandable; I mean, I would never date a trans woman (the whole thing feels a bit too much like dating a cousin). And dating men is hard too-I have NO interest in dating someone who is attracted to trans women specifically, and the fact is that most guys won't date a girl if she doesn't look like one. People are only going to be attracted to me if I look cis. Is this my problem? No, in theory it's theirs. But theory evaporates very quickly when I'm all on my own, and the reality of the situation is that I can't expect other people to change. If I'm ever going to find love, I need to pass. It's that simple.
Finally-people who are obviously trans just make others uncomfortable. I'm not saying this in order to insult anyone, and I certainly try not to feel this way, even though I do on occasion. People just...they're really put off by it. It's not shocking; we've been trained since birth to be disgusted at the sight of a man in a dress. I have a friend back at school who is in the early stages of transitioning, and when she's dressed en femme, it feels like she's making it a joke-she wears a cheap, ugly wig, a dress that doesn't fit. She walks around like a hulking, lanky guy. Her voice is the same as it always is. She doesn't even make an effort to be female; all people see is a fake, mockery of a woman. I feel awful admitting this, but I feel uncomfortable around her. Everyone else does. I'm not a joke; I don't want people to see me as a joke. I don't believe in gender; I'd love to see it gotten rid of. But my sex is (or should be) female, and the reality is that we live in a world where people do subscribe to the system of gender; if I have to be seen as one or the other, I unequivocally prefer to be seen as a woman. I'm not a joke; I'm really afraid that people are going to look at me the way they look at my friend.
I'm in the second group, no doubts there...the issue is that I'm close-ish, but not there entirely. I have a good face, but my brow is really heavy. My voice and body-language are pretty great, but I'm six feet tall and my hands are the size of my face. I even have a male digit ratio, if you believe in that sort of thing. It's not like I look like a man. More and more often, I mention it offhand like I've gotten used to doing because hey, everyone already knows, and people look confused. A trans guy once told me when I mentioned my fears around about passing that he had no idea until I told him. I'm getting there, but...I want people to see me as a real person. I want people to listen to me, respect me, and be able to love me. Personally, my fear is that none of these things are going to happen if I can't pass. That, and my constant worrying about my gender is ruining my life. It's just too much time and energy for me to keep doing it.
Thats my perspective on things.