I don;t like the idea either, BUT I like dog poop everywhere even less. In answer to your second point, maybe the reason you have never had a big problem with seeing dog poop is that the CG workers pick up much of it. We have two dogs ourselves and get very annoyed when we try to run our dogs and all they want to do is sniff other dogs poop (and who knows what disease it carries), and we have to watch every step we take.
As the notice says, they regret it has come to this, so do I, but enough people these days have no consideration for others that I don't think having them sign a "pledge" to promise to pick up their dog's poop will have any affect on the problem