I share that guy's thoughts on the issue, - you may do whatever you want to, but don't try calling it "natural" or whatever.
To be honest, Homosexuality is not Natural. Animals have been found to eat eachother, does that mean we should do the same, Animals have been found to produce poison, does that mean we can?. Would I oppose Homosexuality, No I would not, however in my own view, its not natural, sticking your penis into a mans anus, is not productive and is baseless.
I support gay rights and their right to be gay, but no Thanks, I dont fall for that "gays are natural" non-sense or that " gay gene" jibberish.
If I follow your argument correctly, do you both think disability is unnatural too? If so, Ive got news for you:
"Nearly 150 years after Darwin unveiled his theory of evolution, we have yet to grasp one of its most unsettling implications: having disabled children is as natural as having healthy ones. Every new life is a gamble, an experiment with novel gene combinations that could be a brilliant success or a tragic failure" – New Scientist