"Oh, this is absurd/illogical/fallacy/distraction," came the blowback from the "modern" marriage proponent.
I can't figure out why. Is it even incestuous, if the arrangement is biologically incapable of achieving anything in the way of offspring?
Just to refine my point, I was dead to the discussion at homosexuality. Once "anything goes" is fully legal, I'm not tracking any objections to whatever coupling/geometry/number/species feels good to all of the mucous membranes in question.