No one has to "support a gay lifstyle"- all people have to do is treat them the same as everyone else with the same rights and priviledges. Sexuality is not a digital either "perfectly straight" or "totally gay" choice. Sexuality is an analog thing along a sliding scale and homosexuality exists in the animal kingdom as well.
I have seen a few examples of homosexuality in animals, but only when the other option wasn't available. I have also seen bulls and boars beat each other into a bloody pulp.
At any rate, I don't think comparisons to the animal kingdom help homosexual rights very much. For example, many male mammals and birds do nothing to help raise their offspring. Do we then use that example to defend deadbeat dads?
As my last comment on this- homosexual behaviour in animals (including primates) is not contingent on a lack of choice of partners- it appears to be innate.
If you think that being gay is a matter of choice, ask yourself: when was the time when you found yourself equally attracted to both genders but made a conscious decision to go one way or another?
I agree that it's not a choice - I would just be careful about comparisons to the animal kingdom.