You do understand that you’re misusing the slippery slope logical fallacy, right? A slippery slope logical fallacy is where you argue “A therefore B therefore C” where B does not necessarily imply C.
However, if A does imply B and B does imply C then A implies C. The inevitable outcome of decoupling marriage from heterosexual monogamy is multiple-partner arrangements. Pointing this out is not the slippery slope logical fallacy.
Asher, not all monogamy is heterosexual, as you must be aware. Homosexual marriages are also monogamous. So you can only say that multiple-partner arrangements result from decoupling marriage from monogamy. But that is of course obvious.
Thank you XAU. I see absolutely no overlap between the two groups, except in a couple of cases where polygamous marriages originating in group 2 are recognized by countries in group 1. This should assuage Asher’s anxieties about the slippery slope.