To put it less subtly
Personal responsibility is great! But not everyone has any.
If your neighbors walk their dogs on your lawn, or throw their beer cans out the windows driving thru the desert, what do you do? It is great that some of your fellow citizens take care of their own dog crap and beer cans. But if you don't have a way of dealing with the assholes then you have to resign yourself to live with endlessly renewed piles of crap and deserts filling up with beer cans.
Again, what do you do about the assholes?
PS: In case that was still too subtle: I used beer cans and dog crap to stand for all things ecological. There are more important things to worry about than these.