Moving value cross-chain is itself a violation of sanctions. If you start up a new Tornado.cash instance, you're still probably not going to get touched by the rest of the financial network. Risk departments are going to have dig into the details, and legal (if smart) will steer clear. Further, law enforcement will likely root out and make known to Treasury any additional instances of the same infrastructure they uncover, given that inevitably, the usual suspects will be running things through said channels until caught if they don't.
...And you will be hard pressed to find a judge that has the gumption to go so activist from the bench that they go against what Congress has already authorized.