[Ken Maltby]

In the case of the Seattle legislation:

You have a situation where some engaged in activity that you have local ordinances
against. They are advertising their existance and providing contact information.
So... your best idea to catch these violators is to shut down the sites? Have you
considered the old adage "Follow the Money", anything bought through the internet
creates an electronic trail that has to interface with legitimate financial institutions,
who will respond to a subpoena. When you arrest the last criminal putting up their
site(s), the sites will be gone. If a new criminal starts that sort of operation you
have a good chance of finding it, and them.

As to these efforts in general:

Of course, that wouldn't be the point if your real aim is to gain control over the ISPs
that provide for establishing all sorts of sites, for your own purposes.

Luck;
Ken