> using violence of people who didn't share their politics (politics of genocide).

The genocide became widely known after the war had already started. The allies did not join the war out of their goodwill but rather due to their own geopolitical and economic interests - they never intended to stop any genocide (the US engaged in eugenics and mandatory sterilisation and only stopped because hitler did it too - they even put the Japanese living in the US in concentration camps), it was just a side-effect.

Regardless (and this is a bit offtopic), I wonder, would you support WWII if only to save people from genocide? In the same spirit would you support war against China in order to save the Uyghurs and other suppressed groups? I personally would reply yes to the first one but I am debating about the second.