Would you rather have the US be a willing enabler of genocide, or see that money spent for the improvement of conditions for the USians who paid the taxes?

I don't think the US providing military support to Israel makes us a "willing enabler of genocide," and I think that there are significant foreign policy interests that are probably still being advanced by having a militarily powerful counterweight in the region.

As to the first, genocide is determined by the intent of the military activities - not just the impact of the activities. All warfare displaces civilians that are in the combat zone, and nearly all warfare results in civilian casualties if they are in the combat zones. There have been allegations that Israel's intent is not merely to destroy Hamas, but to eliminate the Palestinians from Gaza. This is a contested point, especially since the Israeli government (as opposed to some individual ministers) cannot plausibly have believed that the actions they were taking could or would result in the elimination of Palestinians from Gaza, given that Egypt would never ever ever take them in.

As for taxpayer dollars, one of the main reasons the US has maintained military support for Israel is to provide a counter against Soviet, and later Iranian, hegemony in the area. That remains. It benefits us if one of there is a really strong military power in the region that is not allied with either: i) Russia; ii) Iran; or iii) China. Reasonable minds can debate whether it is worth it for that money to be spent keeping Israel the strongest military power in the region, but that's the reason we do it - so that there's a massive obstacle to any of those three countries doing what they will in the area. It's a monkey in the wrench, a fly in the ointment, that keeps those other countries from being able to effectively consolidate control over the region.

Changes over the last three decades have altered that dynamic considerably, of course. The fall of the USSR, but the rise of Putin, has changed the shape of the Great Game as it's played in that region, but hasn't eliminated its importance. The rise of China, and their relationships with Gulf States, adds a new important dimension to having Israel as a massive military power (relative to the region) that isn't in either of their camps. And of course, the destruction of Iraq as a check on Iran raises the importance of having another big military player that can counter their ambitions in the region.