It's a complex question, and there were a lot of factors. Certainly the communists were a huge part of it, and the Red Front fighters were almost as big of troublemakers as the SA was. Their reputation was even worse. However, the German economy was also in horrifically bad shape especially on the inflation front, and the people were humiliated by and massively pissed off about the Versailles Treaty (and rightly so). They wanted radical change that got the economy under control and restored national pride, and the Weimar leaders has blown their credibility on both priorities. So my guess is that Hitler or somebody like him was coming to power either way - even without the communism factor, as big as it was.
