I will try to take a shot at answering your questions:
1) They (politicians and financiers) let it happen because they themselves benefited from the bubble(s), their holdings appreciated, because it was good politically to subsidize the American people to live beyond their means, and mostly because they do not understand.
2) America was (is) still living beyond its means by over-borrowing from the rest of the world, the government, the people, the banks, Wall Street all have devoured world savings for many decades.
3) America has (had) all (most of) the guns - most people do not understand the situation. It is the same in Iraq, except in Iraq America actually had to use the guns
4) One way or another, they helped several American generations rub the rest of the world off the savings to live well - beyond well ... so, in a way, they thought they deserved to be thanked.
It is not just the greed of the bankers ... everyone is involved - from small investors, home owners, small banks, etc. But I suspect that people understood / understand. Very few do. Even now, we have to all cover up otherwise the Global Economic system will collapse if the right info is widely understood / shared.
About Alan GreenspanRead the Article at HuffingtonPost