They are an absolute scumbag. It's really simple: in matters where doing the right thing is doing nothing, it means that you went out of your way to be evil. There's not even a self-interest vs. public benefit argument to be made in defense of prop 8: No one gained anything from banning gay marriage. No, the sole reason to vote for prop 8 was "I want to make people I find weird's lives worse". And that's scumbag behavior.

If your political views are "lets abuse a minority because I find them weird", those aren't merely political views.