There’s no doubt that the ICJ has well-known limits in the enforcement of its decision, and countries have ignored ICJ rulings in the past (notably the US, as you mentioned). This to me is not a failing of the idea of international law regarding the prevention of genocide but a failing of nations who would rather exist in a world absent of law since they are able to use violence to inflict their will on others. The problem as I see it with this line of thinking is that abandoning the pretense of international law rather than attempting to bolster it as an international community makes all people in the world vulnerable. The status of nations who violate ICJ orders do not exist in a permanent state of their relative power and could suffer the consequences of a lack of international law when situations change and once-invulnerable bodies become vulnerable. I believe in the basis of the legal prevention of genocide by the international community.
This being so, I believe that there are other consequences for nations found plausibly guilty of heinous crimes in an official international court of law pertaining to laws partially written by the state of Israel itself. Israel depends a great deal on its international reputation. A reading of its history of strange bedfellows reveals this desperation. Being plausibly guilty of genocide is not good for Israel’s relationships or economy. If Israel is concerned about outside threats, scuttling itself in the name of persecuting Palestinians is not a reasonable path. Only the far-right sensibility that Palestinians are inherently unworthy of sharing a country with European colonists keeps Israel from ending apartheid and granting Palestinians full rights as citizens of a unified state.