Right. I finally figured out what my problem with transgenderism is. I don't think gender matters. Just like ethnicity or sexual orientation. It doesn't matter. You are not your gender, your ethnicity, or sexual orientation. You are independent of these things. They affect you, shape your life to a certain extent, but they are not fundamentally you. They are just aspects of you, and in a perfect world they would not matter one bit.
In a perfect world a gay guy would live a completely normal life, and the fact that he loves men in a sexual manner wouldn't matter. It would be as important as him having brown hair. In a similar manner, ethnicity and gender wouldn't matter.
So my problem with transgenderism is that gender and sex becomes too.... important? Sex is a biological thing. Gender is a social construct. Ethnicity is a biological thing, but its also a social construct.
An African child adopted by German parents become socially German (he thinks and acts like Germans). You could be sexually male but socially a woman(you think like a woman and act like one). But the German African shouldn't attempt to change his skin color, just because he's white culturally. Because then skin color matters, and it doesn't. Similarly, why should someone who is socially of a different gender attempt to change their biology? Then you are implying that your genitalia matters, but it doesn't!
I would be against my friend changing his skin color, just like I would be against my friend changing his genitalia.
The fact that my German friend has dark-skin color doesn't matter, doesn't change who he is. If someone said they find people with dark skin color attractive, it point them his way (depending on who he found sexually attractive) . If someone told me they find people with male genitalia attractive, i'd point them to my other friends way (depending on who he found sexually attractive).
The problem for me occurs when a transgender person thinks that they have to change their biology, just as if a person felt that they HAD to change their skin color. Neither genitalia or skin color matter. Be proud of what you have. By trying to change it you are attaching to much importance to it. Breast size doesn't really matter, neither do skin color, genitalia, hair color, ethnicity, etc.
But I personally have a thing for people of northern Asian ethnicity with female genitalia

. 'Course, in the long run it's their personality I stay for.
I know that there is a huge flaw in my argument, but I'm to tired to sit up and figure out how to defend it.
If it doesn't matter, then why wouldn't I date a MTF?
Here is a short version: Because to me personally it matters. And because I feel that being socially male or female isn't binary, there is no such thing as being male or female psychologically. It's just a term we use to define people with certain behaviors. When I say that I'm heterosexual, I mean that I like people who have female genitalia, not people who have the socially defined female psychology. A transgender person is still biologically male, his psychology doesn't matter when it comes to sexual compatibility, his genitalia does.
Since I'm hetero, the person I date must for me must first be biologically male. After that I can find out if we're socially compatible.
Finally: I don't know what kind of brain I have. I don't think my masculinity or femininity should matter enough for me to change my body, and I don't think anyone should let it define them.