I feel bad for cops sometimes, honestly. Trying to de-escalate a confrontation proactively is exactly the alternative to busting heads most of us want to see, but preemptively arresting someone when no crime has been committed isn’t legal. Yeah, their hunch was probably correct that the guy was going to go stir shit up, but until he does they have no right to detain him.
The solution is that they should learn from actual deescalators. A lot of protests I see now have folks in safety vests who cool things off and separate people when someone tries to stir up conflict. But I think it takes an emotional tool kit that isn’t currently common within police training.