Do you think that if that was the 'only' thing that Hitler and were guilty of that Britain would still have gone to war with Germany?
That has nothing to do with whether we are entitled to hold a view on their behaviour. We cannot go to war with everyone we disgaree with over every issue can we?
But the answer may well be yes
We went to war because they invaded countries far removed from Britain.
Quite possible that the allies (not britain alone without the strength at the time) would have taken action if it had simply been the genocide in place