It comes from the position that gay marriage itself is an abomination, thus allowing it will open the door to other abominations -- like marrying multiple people, your dog, your toaster, etc.
Nope. This is not true. Polygamy is not necessarily an abomination is my eyes. Many Biblical patriarchs married multiple women.

You are attacking my argument as unsound by using reductio ad absurdum and including all kinds of ridiculous scenarios I never mentioned. Perhaps we should just stick with the actual points made.

I have no issue with Greg or anyone from a religious perspective having those feelings, though I am encouraged by the Pope and his recent stances on the issue. I do, however, have an issue with meaningless debate points that are wrapped in old school thinking of scaring people.
This take sounds very much like how liberals respond to people who are against the ACA or other liberal policies; scaring old people, etc.

I am not trying to scare anybody. I made a valid point.