> Nothing stoping Russians from starting sabotage operations internally in protest.
A lot is stopping most people.
First you need somewhat objective information what is happening. A vast majority of the population does not have that. All independent voices have silenced, except if you are a political activist and know what to search for.
Then you need to take significant risk to commit crimes. As a small saboteur they won't have Novichok for you, but Russian prisons are very close to systematic
torture. Especially for prisoners with a political background.