The idea that Hitler, Tojo, Stalin and Mussolini are among the most evil leaders of all time - and that people like them must be stopped at all costs - is a relatively recent idea.
It is an idea promoted by people like you and I, who statistically speaking, weren't likely even alive when WWII ended.
Thus we never had to do the hard-lifting of deciding just what to actually do, or not do, about these obviously aggressive tyrants.