What does it mean to be politically existential? The question of homosexuality and its origins is a good avenue to attack the question.
For some time now the debate over gay marriage and gay rights has been centered on the question of the origins of homosexuality. Those who support gay rights, generally, make the argument that because homosexuals (in their view) are intrinsically gay-- or, less charitably worded, forced to be gay-- we must permit gay rights, gay marriage, gay adoption, etc. Traditionally, opponents of gay rights and gay marriage, in contrast, have asserted that homosexuality is a choice, and that as a choice, it has moral content-- and in the minds of those opposed to homosexuality, homosexual acts (or lifestyle, whatever that means) has negative moral content.
The degree to which someone is predisposed to homosexual behavior is a scientific question and one which I am not equipped to answer. It seems very likely to me that there is some physiological connection behind homosexual attraction. Note, though, that the fact that something is physiological doesn't necessarily mean it is necessarily genetic. The older brothers hypothesis points to a physiological origin, but it is not genetic; rather, environmental factors (the number of older brothers, and perhaps the presence of anti-male antibodies) in this view cause homosexuality.
Note also that there is a large difference between saying that something has psychological factors, and saying that it is a choice. Consider schizophrenia. (Please note that I use this comparison not to insinuate that homosexuality is a mental disorder, but only to talk about similar combinations of psychology and physiology.) The best current evidence on schizophrenia, as I understand it, is that there is a combination of genetic predisposition, exposure to certain environmental factors, and psychological factors at play. Saying that there is a psychological component to schizophrenia does not mean that schizophrenia is a choice. That false dichotomy, between pure genetics and pure choice, has dominated the debate on homosexuality for too long.
Personally, I imagine that the origins of homosexuality are likewise a combination of genetics, environment, and psychology. I think the idea that it is purely genetic in origin is just as reductive and stupid as saying that it is purely a choice. But as I said, it's an empirical question, and one I don't have the answer to.
But in the larger philosophical sense, it is immaterial what creates homosexual attraction. The fundamental idea of existentialism, or my kind of existentialism, anyway, is that we must judge people by their actions, by their choices in the world. And-- this is where things become controversial-- whatever is true about the origins of homosexual attraction, homosexual behavior is the product of choice. People choose to have sex, just like they choose to do anything. Whatever predispositions a person has to any kind of behavior, there is still the choice. In the age of genetic determinism, which tries and tries to reduce people to objects in the world, which seeks to rob them of their freedom and responsibility, this fact must be remember. Whatever dispositions to certain behaviors exist, the individual still faces the choice.
Now, certain choices are harder or easier to make. Certain people really have more or less difficulty in choosing a certain path. The alcoholic indeed has a harder time choosing not to pour the drink. But he still makes the choice; he still directs his own behavior; he still has dasein. None of the genetic determinists can change this fact, not Steven Pinker or Charles Murray or Steve Sailer. I don't believe in racial predisposition to lower IQs. But suppose that theory is correct; it remains immaterial. The black person who takes the IQ test has the same choice in answering the questions that a white person does. He and only he chooses answer A, or B, or C.... According to the hereditarian view, the black person doesn't have the same tools with which to answer the questions as his white counterpart. But when is life ever different? No one ever has identical choices, no one ever makes choices with the same benefits or hindrances. What everyone shares is the choice, their ability to make sense out of their own life through their conduct in the world.
So that probably means I'm opposed to gay rights and gay marriage, since I think people choose whether or not to have gay sex, right? Not at all. I support gay rights and gay marriage enthusiastically. I simply reject the notion that support for gay rights must come only from a belief that gay people "can't help being that way." My support for gay rights and gay marriage comes from first principles, from a basic belief in the rights of anyone to self-determine, in the notion that an adult should have the ability to choose to have sex with whoever he or she wants, to engage in the contract of marriage with whoever he or she wants.
Consider that vision of gay rights, which says that because they are forced to homosexuality, gay people should have the rights. What an incredibly insulting vision of homosexuality! Gay people shouldn't have rights because they are gay and can't help it. They should have rights because they are people. What could be more insulting that saying that a person is the way they are because they can't help it, so we should let them be that way?
But this is worse: that vision of homosexuality, supposedly supportive of gay people, consigns gay people to the status of objects in the world. They don't choose to act, but are vessels for the desires of their homosexual nature. They don't choose and maneuver through the world; they are moved by their nature. They are denied their humanity because their actions are considered out of their control.
Another consequence of the existential is that, because we must always judge someone by their behavior (and not "what they are"), we can never consider a person defined until their death. You are never done with the process of making yourself. In that sense, then, there is no such thing as a homosexual; there is only someone who has participated in homosexual activities. (Just as there is no such thing as a straight person.) Now, in day to day life, do I use the term "a gay person" or "a homosexual"? Sure, just as I use the words "a liar", "a plagiarist", "an ethical person." But I remain open to the fact that their behavior is not finished, that they are not complete, that they are not an object in the world.
This fact is why I am often bothered by the close-mindedness of many people who self-identify as members of the gay community. Many gay men (there I go again) tend to deride the idea that a man who has had sex with other men can be anything other than gay. We understand that there are men who have had sex with women, gotten married to a woman, and had children, who might later self-identify as gay. But the reverse tends to be dismissed as self-hatred, self-denial, a closet-case. I don't understand why a movement that believes in sexual freedom and the right to self-determine seems so ready to confine some to definitions that they reject.
The thing to remember, if you think like me, is that no one has ever become anything. They are in the process of becoming.