A great deal of evidence does exist that homosexuality is genetic. But as a disciple of sociology, I tend to pay a lot of attention to the actual difficulty of determining whether something is genetic or cultural.
To a certain extent, there is culture involved. Until individualism really caught on a century or two ago, there was no distinction between "homosesuals" and "heterosexuals". There was simply normal and deviant sexual behavior. An act of homosexuality was not considered a part of a personality, but a sin or social taboo.
Whether it is genetic or not, there is a choice in acting upon the temptation. Thus acceptance of homosexuality does cause more of those with a propensity for homosexuality (genetic or cultural) to act upon their feelings. Also I have known so many bisexual girls in high school and men who actually committed gay acts to earn their attention, that I am suspect of some social influence. Though most of them who I still know have since "become" heterosexual.
I still fail to see, whether choice or genes, what this does to hurt society. Out of all the gay men I know, not one is into converting straight people as some people seem to believe they do. I think discrimination and violence of any sort are more destructive to society.