it's certainly shocking to hear that un workers were involved in the carnage, but i haven't seen any evidence that it was organized by unrwa management or any good argument to blame unrwa itself for what happened. if the concern is that it's been infiltrated by hamas, that is a broad concern that needs to be more coherently addressed; hamas needs to be destroyed, but unrwa is, on it's face, a secular aid organization and the kind of group that should be funded to counter islamicist influence. the american right has been keying on this group for decades and the fact that it isn't christian probably is a key part of that.
state funding in the levant should go strictly to secularist, non-faith groups in order to incentivize them to move away from their faith and the un is the right body to organize those groups.