Read it again. He’s using incitement to violence as a consequence to to be avoided, not as a driving factor.
He's explaining the why. That statement is there for a reason, and your reading implies it's superfluous.
He was writing at the end of WW2. He was saying it would have been fine to stop the Nazis at the start, before they were inciting violence because they couldn’t be reasoned with.
The National Socialist German Workers' Party employed violence well before they achieved power. Popper's warnings are obviously an allusion to the Brownshirts.
It’s clear you don’t agree with his position , and that’s okay. You can just disagree with him.
This is catty. Like a little girl. I've extended you courtesy and I would appreciate reciprocity.