That's wrong. With the Bayesian interpretation of probability, you can assign probability to any event. In fact all certainty about belief is just probability

That's wrong. With the Bayesian interpretation of probability, you can assign probability to any event. In fact all certainty about belief is just probability in disguise. There were betting markets for the brexit vote. They assigned 25% probability to brexit. Of course markets aren't perfect. But anyone who really believes they know better should be able to get rich off them. And somehow that doesn't happen. So they are the best estimates of probability we have.