Okay? Did I say there were not?
Yeah, it can be brought up to support it. It's brought up when someone says "It's not natural." It's not the entire argument, but it's one argument specifically for when someone says it's unnatural. Homosexuality isn't inhumane, so the argument "Natural things can be inhumane" is not a good response.
Animals are run completely by instinct and nature. If it can happen in nature without outside interference by man, it's natural, and homosexuality falls into that category. Sorry to burst your homophobic bubble, Yubel.