Did the Allies think the Treaty of Versailles was really worth the Lebensraum expansion as well as the Holocaust?

The Allies supposedly thought Germany committed a whole host of sins during WW1. But I'd say, compared to WW2, they weren't even all that bad. It was nice to deal with a non-antisemitic Germany that wasn't controlled by a megalomaniacal dictator probably. And all they had to do was not punish Germany so unbelievably harsh, yet they went forward with it anyway.

If the US can be blamed for ISIS "because the US made the choice to destroy Iraq" why can't the Allies be held accountable for WW2 and the Holocaust since the massive resentment that got created inside the hearts of Germans all started with the Treaty.