So why doesn't Israel do "whatever the hell it wants" if it has the US protecting it?
It pretty much does. I can't think of any instance where Israel had to restrain itself out of fear for a UN intervention, can you?
The high number of USSR vetoes might have to do with the facts that a) the UN as a whole was dominated almost entirely by the West and its allies untill the great decolonisation waves made the numerical balance of power shift towards the Third World. A fact the US was quite adept at exploiting, as evidenced by the way they played the institution during the Korea War, and b) the USSR was completely on its own in the SC well into the '70s, as Taiwan had the Chinese seat in that council and wouldn't give it up untill, what, the Shanghai Communiqué (?) (Honestly can't remember, I suppose it
must have been then.)