Socialism, for one.
Socialism with a provision which allows for private capital and the profitable investment thereof.
How about limits on "leverage"? Instead of allowing a person to borrow 90% of the cost of a derivative, maybe make them post 80% of it? The sort of thing learned from the Great Depression which was circumvented by those clever Conservative rascals.
There are a lot of ways. Greed isn't bad, per se. It's when massive egos take huge risks which fail to the detriment of others besides themselves that it's bad.
Arf (It's one of the Seven Deadly Sins, Bow. Yeah, they don't care about that - beyond 'em.)