That would result in the USA going to war against the UN. There is a reason the UN only takes action when the security council agrees. Countries on the security council can plausibly use their military might to prevent any UN action, so to prevent the senseless deaths of peacekeepers, they are given a verbal veto instead.
I tend to agree. The US bears a pretty large amount of blame here and I don't think Israel would have continued their aggression had the US withdrawn aid (or threatened to). But if they had continued, then that's where UN peacekeepers should have been deployed.
