Same way people throw plants away, I think. Our gardening hearts are just too big to do that.
I can't even imagine letting go of either a plant or an animal. Of course there are issues that must be considered, aggression, proximity to children, that kind of thing; but I like to think in that situation I'd find a pet a home.
I happen to know the former owner of Mambo; he is a local attorney. My son lives in Indianapolis and has for years, so he didn't know, but at the shelter they'd told him the owner's name. I knew of him. It seems fitting somehow that Mambo landed in my son's life; my son is an attorney too, but of a whole different breed. I doubt very much he'd ever 'throw away' a pet or a plant. He isn't a gardener either, my son, but he sure was raised by one.