I don't think we have those here. Maybe I just never noticed, but I don't ever remember seeing a license plate with anything like that. Bumper stickers yes, but not license plates. But it does seem to me that both sides should be covered.

I agree, both sides should be available. Or, neither side at all because we don't need more road distractions. If I saw a plate with some sort of hateful message about gay marriage, or about Native Americans, or women in the work place, it sure would get my mind off the road and thinking about rear ending the jerk.
I completely agree. I think we have enough distractions on the road, enough road rage already IMO.