Which behavior of the allies are you talking about specifically in Europe? In Japan, the dropping of the atomic bombs almost surely saved a huge number of civilian lives, given how reluctant the Japanese were to surrender. Anyway, there are so many differences that it's hardly worth talking about.

Also, Israel is under existential threat not from Hamas but from too much of the world thinking it is brutalizing the Palestinian population too greatly. Some of its people are under constant threat from Hamas, but the country is not threatened by them at this point. (Obviously if Hamas was allowed to arm itself without restriction, funded by Iran and others, this could change.)

And the U.S. was the only of the allies not under existential threat. All of continental Europe had already been conquered by the Nazis! You can't get under much more existential threat on the country level than having already been completely overrun. And certain subgroups (e.g. Jews) were under existential threat once the Nazis took over. So I really don't see your point. WW2 in Europe was a profoundly existential affair for huge numbers of people.