When I see "pretty much by definition" I get the feeling that someone is trying to disguise their opinion as somekind of monolithic truth.
If BoA can crash the global economy it's because enough human beings personally decided (i.e. not by beaurocratic policy) to trust them. If people lose trust in BoA (i.e. it nosedives, as in the scenario you are describing) customers, clients, investors will stop doing business with BoA. Then their share price drops. Then their CEO panicks. Then the board/investors give the reins to someone they deem more competent.
If the government crashes the global economy (e.g. Smoot Haley) what recourse do you have? You are required by law to pay taxes. You can vote another policitian to come in, but you have to wait for an election. And if both sides fail to produce a viable candidate you're just as worse off.
A more likely scenario is the government just sucks up slowly growing piece of the pie. The economy does not crash per se, but it lurchs at 1-2% and hiring is very meager. This is what happens when the do-ers can't take risks and stick their money under their mattresses.
