Actually zombies are caused by a toxin from a tropical marine fish, kind of like fugu poisoning. But in the popular culture, zombies are actually dead people. And well, we could just conclude that dead people have no rights, kind of like opossums, so they could just be roadkill, for all we care. But they do have a wee more mass than opossums do, could need a front end job afterwards, should you hit one.
Demons in a way are completely different. As they are not natural, I believe supernatural is the keyword, they could be classes as toxic waste, and then line them up for Superfund cleanup. But how would these demons be killed? I assume that what would kill a person or even a zombie would have no affect on a demon. And like Michael just said, what if they run for mayor of Portland, would it make any difference?