Why should it matter if homosexuality is biological?

Let’s say the scientific community comes across what might be labeled, “the gay gene,” or say “the gay marker,” figure out that sexuality is in fact %100 genetics or what have you (there are lots of scientists actively trying to do this).

OK so now homosexuals are “absolved” of all that “sin” of “choosing” their “lifestyle” of enjoying the same sex.

My question: Why do we need the stamp of science to allow ourselves to accept (or worse, ‘tolerate’) other individuals?
In other words, even if homosexuality is a chosen “lifestyle,” or what have you, why should that make me less likely to accept them as a human being whom is just as deserving of rights and respect that I am?

If you want to say it’s because they “choose” this “lifestyle” that makes them “culpable,” I ask: of what? Their difference allows you to make decisions about their life? I think not.