Modern banks are protected by insurance networks more indestructible than adamantium. Even if the world dies in nuclear fire, some exclusive bunker will hold an accountant etching ledgers in his own blood, mixed with engine oil from the ventilation system to make sure it stays in the black.
"I still have all the big numbers, but there's no food left. Luckily, I'm too rich to be bothered by this incredibly subtle moral."
Even if the bank were to fail, the Federal Deposit Insurance Corporation ensures people get their money back. Which means your hero isn't fighting for justice but lowering insurance premiums. Which they'll negate by smashing the place up and killing people. Even the insurance company would tell them to get their ass out of the building faster than the speeding bullets their presence will cause. An untrained uberhuman leaping into a hostage situation is selfish: They're the only person guaranteed to be fine in the ensuing hail of automatic fire.
In Spider-Man 2, Peter Parker endangers everyone in the bank, including his own Aunt May, trying to stop Doc Ock from taking someone else's money. Money Ock would otherwise have mechanically strolled off with. Nobody died, no thanks to Peter "Let's start a fight with the homicidal maniac in a crowded civilian area" Parker, but the collateral damage easily cost more than could have been stolen. They took out dozens of apartments and cars in their building-side battle. They were barely out the door before they destroyed a taxi. Which brings us to ...