It's the same standard the entire world held the US to after 9/11. A response to the attacks by Al-Qaeda was justified, the 20 year "Crusade" across the Middle East was not. A response by Israel against Hamas terrorism is justified - a campaign of extermination and genocide is not.

It isn't even a high standard, "don't commit genocide" has been the bare minimum requirement for any modern country, much less democracy, for nearly a century. It would be antisemitic to believe that Israel is uniquely incapable of meeting that minimum standard.