"Some of these issues are so important you can't not speak out"
We live in an age of hyperpartisanship, for better and for worse, and a part of that is tagging the opposing team. It doesn't really accomplish anything, but it feels better when you're the side doing it. Sometimes, when it seems the whole nation is against you, seeing an opposing viewpoint that mirrors or excedes your own is the right thing to keep you off the ropes and in the struggle. Billboards and artwork like this exists for the same reason cheerleaders are a big part of professional football. And generally about as helpful in the final result. (And in the event anyone thinks I profess this because it's Trump, no, it isn't.)