I thought the bag banning was the wrong thing myself. I always reused my grocery bags as trash bags, now I have to buy trash bags...which seem like they use more plastic. But maybe most people don't use them that way.
I did this too, but I only needed a trash bag like once a week, and inevitably ended up with more than that, before I got diligent about reusable bags. Even if everyone did it, there's no way every bag would be accounted for.