Yeah, presumably the First Amendment allows for actual real life CP to be banned, so I'm not sure it's relevant here.
Anyway, I think if it leads to paedos being more likely to move on to real kids, it should be banned.
The First Amendment protects speech as well as art/porn and I think sex dolls would fall into the latter category. Real child porn is banned because children cannot consent. Fake porn doesn't cause demonstrable harm to any human being in its, erm, production.
Why would they make pedophiles more likely to prey on real children? The purpose of the dolls is to deter would-be predators so that their perverted fantasies remain just that - fantasies.
I agree with Cath that they shouldn't be available on-demand. Should psychiatrists be required to write prescriptions for child sex dolls? I dunno. I doubt anyone's gone through the lengths to study it, but until science finds the 'cure' for pedophilia, then the dolls are probably the best available option.