"I repeat what Keith said,…."so anything is permissible so long as we do it?""

I'm not interested in arguing philosophical points, I can see you won't be persuaded.

I am however stating the fact that sexual behaviour includes activities that goes beyond those required for reproduction: they are also used in bond reinforcement within same-sex groups and the establishment of hierarchies within some animal groups. In fact, 75% of Bonobo sexual activity is non-reproductive, apparently. Do you only use your arms for waving?

This is an observable fact, not an opinion. Google it and read the volumes already published in peer-reviewed journals. Same-sex interaction is widely observed in many animal groups, including humans. It's a variant of normal sexual behaviour.

What is being argued here is how we as a society treat those who engage in same-sex relationships, and I'll leave you guys to sort that out.