Yet earlier, Kid, you say, "The VOTE is that they are NOT voting."
But what Bart describes is not just a protest "vote" - it's shutting down all voting. Voting, in this case, would be to show up in Salem and cast a vote against Cap-&-trade.
The senators are legally required to be in Salem and allow a quorum. Law enforcement can legitimately compel them to be there. Just as it would compel you to show up for, say, court business. It's not a police state to have police enforce laws. An oath of office is legally binding.