They cannot fight their biological destiny, no matter how hard they try, and that is another reason that I believe sex and gender are biological, and not simply psychological or mental. However, I firmly believe that how society looks at gender is social, and has nothing to do with biology or nature. Society has placed certain "rules" about sex and sexuality on men and women. Men are supposed to be manly, strong, the providers, and most of all, supremely "male" and all that means. It means men are supposed to be unemotional, not show their feelings, enjoy sports and violence, and never show weakness. Women are supposed to be feminine, weak and dependent, good-looking, and emotional, and a man who shows these tendencies is labeled "gay" or "weird" by other men. These are all social constructs that most of society firmly believes in and abides by. Thus, anyone who is different from these constructs is considered to be wrong or misguided in some way. Homosexuals and lesbians do not all fit in these traditionally accepted social constructs of society, and that is one reason so many people do not accept them or their lifestyles. They may say it is because of religious or moral grounds, but for many, I think it just boils down to the fact that these people are different, and do not fit the acceptable models of society, and so, they are not acceptable.

I think that gender is what you are born with, no matter what that is, and you cannot change it, at least you could not change it until the last few decades. It used to be that "biology...

This film follows the life of a man, who attempted to live as a man and simply could not do it. He even fathered a child, and never knew it. Now, he is living as a woman, and has had all but the last operation to transform himself physically into a woman. Today, it is possible to change your sex, and many people do it because they know themselves and their desires and needs, and know that they were born into the "wrong" body. Gender is conceived at the instant of conception, but the person living inside that body still may have different ideas and conflicts about their gender. That is why sex and gender are really two different things. Gender is what you were born with, but sex is what you really are in your heart and soul. If you are born in man's body and never feel comfortable in it, then your sex is really a woman, and you should follow your mind and your heart. It is difficult to be different in America (and in many other countries, as well), but it must be even more difficult to live inside a body that you do not feel comfortable in or enjoy. Gender is biological, but all the rest is societal, and that is why people should learn to be more accepting of gay people - they simply cannot help who they really are.
References

Transamerica. Dir. Duncan Tucker. Perf. Felicity Huffman, Kevin Zegers. The Weinstein Company, 2005.

Vincent, Norah. Self-Made Man: One Woman's Journey Into Manhood and Back. New York, Penguin, 2006.