Preference is one thing. You framed it as a moral stance, that's religion whether you want to be religious or not. But please, keep going. The fact that you can't tell the difference between "we're apes, there is one naturally monogamous species of Ape, and it isn't H Sapiens" and a bunch of rules that Bronze Age goat herders made up to increase the price they'd get for selling their teenaged daughters to their middle aged neighbors is fucking hilarious to me. One of those is a religious belief, one is not.