There is a big relevant difference between Israel and the United States, on the one hand, and Hamas, on the other. Hamas is fighting a war of national liberation against an illegal and immoral occupation. Israel and the United States are each involved on the other side, the side of the oppressive occupiers. Hamas has limited resources to resist the oppression, while Israel and the United States have unlimited resources to oppress. No one is allowed to mention it, but Hamas possibly - I would say probably - has a right under international law to target civilians if that is the only weapon it has to resist the occupation. International law is mostly how the international community reacts. There are and have been many respected world leaders, including many from Israel (although it is highly debatable whether the creation of Israel was a war of national liberation), who spent their younger days targeting, and killing, civilians (e. g., Menachem Begin). As long as you win the war of liberation, the international community seems completely accepting of the concept of targeting civilians. Of course, we're not supposed to mention this, as it doesn't sound very nice.