Most of the reason not to want a post-op transwoman is cultural. Pre-op, it makes some sense (we all have a right to be attracted to certain plumbing) -- or if a man wants to have biological children with his wife/girlfriend -- but a lot of guys are honestly past these notions or feel a need to overcome them on principle. I still marvel at these men some times, but I don't think it's terribly hard to understand their positive reception.
I personally have two guy friends who surprised me and are okay with women like us - and not just for a sex. One of the two came around gradually as he spent more time around me, and he's known me since long before I came out. He's my oldest friend, and has expressed attraction to me. There are definitely guys out there who simply have a very fair and well-adjusted world view. I have definitely noticed a correlation between men with a healthy view towards women and men who are okay with trans women. I hate to drop this bomb, but I think a lot of the guys who aren't okay with post-op ladies are prone to objectifying women. Because we don't meet their empty objectifying standards, they turn away from the rest of us.
I recently had a guy fall for me who, when he found out, said it could never be. He still wants to remain close friends with me and he says he feels "deeply ashamed" of the way he feels, but that he can't help himself. He admits it's learned behavior and says that "it's not you who's ***** up [my irl name], it's the rest of us." It still really hurt and made me feel hollow to him, but right after I met a guy who's okay with it even though I've still got the "wrong" parts (and I'm fairly certain I'm not a fetish for him). It's been another step that helped make me feel like accepting men are more common than you would expect, and that the ones who can't dive right in are becoming more comfortable with at least respecting us.
Some guys are open to it but only after learning more about your particular type of womanhood. For starters, when talking to them, I never say "I used to be a boy." What's in my head and what's in my heart were always there. As I mentioned earlier, I've still got my extra bits, but in the future I intend to say something like, "I didn't always have a vagina." A lot of it is in perspective, and most guys still want the impression of a lady regardless of her history. Right now I just say, "I haven't always presented as female"; I think that's probably the most comfortable way I've found to inform men so far.
As MaidofOrleans put so well, there is so much more to you (and any other woman) than trans or not trans. You're a person underneath (or perhaps above) all that and still a woman. Many men want good women that they have fun with and enjoy as people, plain and simple. If you're one of those women, a lot of these men can look past what is truly an empty characteristic. Honestly, I almost like to think of being trans as a screening system for objectifying/insensitive men.
Like you, there are still days where I wonder at my own authenticity as a female and question if I'm really valid for the men I interact with. It happens, I think it's always going to happen to people in our position from time to time -- but when it comes down to it, I really think it's just a self-defense mechanism. It's hard to accept what we are and how people will (likely) always treat us. It's hard to keep it a secret and it's even harder to spill that secret to someone in a gamble for their love. Some times, I think that telling ourselves that none of it is true, that we aren't really valid, feels a lot easier than going through it at all. At least that's how I feel.
I hope this helps somehow and that your feelings pick up a bit!
P.S. I'm glad I'm not the only one who calls herself a "->-bleeped-<-" in self-depreciation and then tries to shamefully (comically?) brush it under the rug.
