I believe this is what they call "raising the stakes" and the consequences of this may not be what you want/expect. In fact, taking such an aggressive move may hasten the very thing you're trying to prevent.
Let me elaborate. Right now most politicians in the US are pretty out of touch with the Internet, that much we can all agree on. They hear that it's powerful, and they have young staff members saying how the Facebooks and the Twitters are necessary nowadays, but it's easy for the regular politician to not really buy into the hype. Despite that politicians (and nefarious people in influential positions) aren't really happy with the Internet and the whole open thing. Which is precisely why we're getting SOPA. Now, US politician attacks have thus far been limited media copyright and piracy, dabbling a little bit into privacy with the Facebook stuff. These are easy targets.
Now, if these sites take this kind of action, and has the kind of effect that you want - namely kicking these politicians out - you don't think every other politician is going to learn a very big lesson. And I'd hope that we plebes have also learned a lesson. When politicians/people in power have a "threat" that they are actually vulnerable to, they don't respect it and learn to co-exist. Instead they try to destroy, co-op, or otherwise remove it as a threat.
Maybe I'm being cynical/pessimistic, but given the history of humanity and the way people in power behave, I think I have reason to be.