What if Isaiah Berlin Was Right?

Isaiah berlin was famously critical of liberalism as a massively failed experiment that leads to weak societies. He saw all the tolerance, multiculturaism and limits on government power get thrown out the minute a true political disagreement comes to pass. Maybe it's not a fundamental part of human nature to descend into violence whenever political differences get really serious? What might the twentieth century have looked like if we had listened to and been tolerant of ideas that made us uneasy?