Shapiro's argument isn't the worst he's ever made, I assume most of his listeners and the posters saying to watch his video didn't know the political history of Weimar Germany, that there was a low level civil war happening in an already failed state. (I know I've made this information available to NeoGAF.com users countless times with them ignoring it.) I think it's a stretch to argue that's what led to Nazi victory and that any kind of similar action (let alone current actions) by AntiFa against white supremacists will lead to the Nazi's/"alt-right" becoming more powerful in the U.S.
He gets too distracted off into making it about defending the statues and modern politics and stuff for the remaining 30 some minutes. But before he left the topic he should have pointed out that the Weimar State was actively arresting and attacking both Nazi's and Communists as the two groups fought their war. It was a three way war and the Republic's ruling forces were losing it both literally and electorally, the Nazi's and Communists wound up with a negative majority in the legislature. That's why it fell back on ruling by decree, and increased force against the Nazi's and Communists. It wasn't the people who decided the Nazi's were more acceptable because the Communists/Anti-Fascists were causing more violence, it was a gambit by the political elite that Hitler could be controlled because they didn't take him seriously as a politician or person, they didn't think this of the Communists and supported shutting them down as well.