Totally in agreement with you. I saw a woman letting her dog foul in someone's drive the other day. I haven't got a dog (grew up with them though) but would it not be possible to put the bag down under the dog's bottom so the poop lands on that? Because even if the owners clear it up there's still a bit of a mess left. Someone needs to invent a bag on the end of a stick that starts off as a big of flat plastic that you put under the dog's bottom then pull a handle to gather it all up and then press a button to drop it in a bin.
The bridge over the railway line in Wandsworth Common stinks - not sure if it's dogs, foxes or humans but it's pretty disgusting. I can vaguely understand that when people are exercising their dogs on the common they might miss the fact they've pooped but when it's on a pavement and the dog has to be on a lead it's just unbelievably anti-social not to clear it up. It's particularly bad around the kids' school - I'm sure people do it deliberately.