Being gay is a choice

Claim
Opponents of gay marriage (and homosexuality in general) often argue that being gay is a choice, and that this somehow proves that the gay lifestyle (and gay marriage in particular) is illegitimate and should not be given any legal recognition or protections.

Scientific evidence disagrees
Scientific evidence currently disagrees with this conclusion. Although there is as yet no evidence that homosexuality is genetic in origin (and it may in fact turn out to be the case that there is no genetic component), there do seem to be significant physiological differences between homosexuals and heterosexuals, much as there are between transsexuals and non-transsexuals: "...notable differences between the physiology of a heterosexual male and a homosexual male. These differences are primarily noted in the brain, inner ear and olfactory sense." (While the experimenter himself argues that it would be a mistake to conclude "that gay men are born that way" based on his experiment, it's not clear that any other, contradictory conclusion would be more reasonable.)

Point is irrelevant
Whether or not it is a choice is irrelevant. Arguments over whether or not is is a choice, valid or not, serve only to muddy the issue; the only relevant question, as for any activity which some people do and others don't, is whether it is good or bad.


 * If it is bad:
 * If it is bad and involuntary, then there should be research to help overcome it (e.g. alcoholism, smoking) – as indeed was tried for many years with homosexuality, with much harm done to those supposedly "cured" (see Homosexuality and psychology) and as is still being practiced in a much less scientific rational, and humane way by the fundamentalist Christian ex-gay movement.
 * If it is bad and voluntary (i.e. "a choice" -- e.g. drinking alcohol or smoking for the first time), then we need to both have a clear understanding of (a) why it is bad and (b) why individuals nonetheless desire it. (Until you understand the latter, you haven't conclusively answered the former.)
 * It would also be advisable to compare with how the law handles other "harmful but popular" activities; smoking and drinking, for example, are heavily restricted but not illegal. Smokers are not prevented from obtaining medical insurance, or prevented from being included on a spouse's insurance policy; the cost of that insurance is simply raised in direct correspondence with their increased likelihood of needing medical attention due to smoking.
 * If it is good, then it should be encouraged, regardless of whether it is a "choice".
 * If it is not clearly good or bad overall, then it should fall within the bounds of the "pursuit of happiness", which is stated as an "unalienable right" by the United States Declaration of Independence and general freedom of choice.

Reference

 * Wikipedia:
 * Homosexuality:
 * Biology and sexual orientation
 * Prenatal hormones and sexual orientation
 * Homosexuality and psychology
 * Reparative therapy: "The ethics and efficacy of these procedures are disputed, and most medical professionals warn that attempts at changing one's sexual orientation are potentially psychologically harmful. All mainstream health and mental health organizations who have a position on this therapy have condemned it."
 * Rights:
 * Life, liberty and the pursuit of happiness
 * Inalienable rights