Talk politics.

I am not particularly for or against it. The fall of single race marriage laws over 40 years ago did not immediately lead to same sex marriage because law is usually read narrowly --each group has to make its own case, and I have not heard the case so far. The same thing happened in education, by the way -- Brown vs. Board did not lead immediately to full inclusion of students with disabilities -- that was argued in a different set of cases.

I am not opposed, per se, but I think polygamists will need to make some different arguments than same sex marriage advocates did. Assumptions about power of attorney and inheritence are generally fixed on a two person relationship -- in polygamy, that's made more complicated, so there will be some need to work that out in the civil institution that is acceptable and equitable. I'm sure it can be done, but I've never given it particular thought nor have I heard the arguments if they have, in fact, been made beyond "you did it for gays, now do it for us." That's not how gay rights advocates made the case for same sex marriage -- multiple partner marriage advocates have their own arguments to make.