It was a big part of why the Nazi party came to power and why so many people didn't fight back against it people were so disillusioned with politics and the socialist parties had lost a lot of trust.
By the time fascism was on the rise they were just in survival mode because they'd already seen one war and just wanted to survive the next one. It's was hard to get a bunch of people to fight for an idea that has screwed them over already. It definitely wasn't the right thing to do but it turns out not every one is a hero when it comes to fighting oppressive regimes even if they don't like them. Enough people will just keep their heads down and try to survive.
History isn't something that just takes place in books it happened to real people who also play a role in shaping its outcome. The only reason I'm still doing leftist stuff is because I met Eric Hobsbawm (or im pretty sure it was him) and I promised him I'd keep fighting for a better future.
No not the SPD, just out of interest are you american?