Laurence Thomas has an excellent post Are There Gay Animals? On Justifying Gay Behavior in Humans. [If you have trouble accessing the post, see the comments below for how to get it to load properly.] Laurence doesn't think there's anything at all wrong with being gay, but he points out some severe flaws with one argument for the opposite conclusion. Some people, in order to support the view that Laurence holds, point out same-sex sexual interaction in non-human animals. I've observed such behavior myself, so I know it's out there. Several things are wrong with this argument, but I'll summarize two of his points here, and you can read his post for a fuller treatment.
One is that lots of things animals do could be wrong for humans to do. Laurence gives the example of promiscuity. Just because animals don't settle down with long-term partners doesn't mean we shouldn't. There are in fact good reasons for thinking that we should have long-term partners, and these have nothing to do with religion but arise simply from thinking about the nature of human sexuality and psychology.
Another problem with the argument is that it would be thoroughly inaccurate to describe animals as being gay. Being gay is not engaging in certain behavior. It's all wrapped up in having a sexual identity defined in terms of sexual or romantic relations with someone of the same sex. Animals don't do that. They have nothing like the kind of developed sexual identity that humans have (and Laurence gives several examples having nothing to do with gay to show the level of difference between animals and humans in terms of sexual identity).
See also his previous post Gay Marriage and the Argument from Consenting Adults for a criticism of another bad argument on a related issue. Laurence's position on record on gay marriage is the same as mine, i.e. that the government shouldn't be endorsing any marriage but leaving it to religion, while allowing same-sex couples to have inheritance, hospital visitation, health insurance, and other couple benefits. But the mere fact that couples consent to gay sex doesn't at all justify it.