And where do you imagine those gains come from?

If you can buy something and then convince other people it's worth more than it is then you'll turn a profit while screwing those people, sure. But that's true of anything - cars, houses, bridges....

No it's not, your argument excludes factors that are huge in reality. For example, these executives that find themselves in a position to do that usually have only found themselves in that role after an extensive amount of time (10+ years) working for not only that industry, but that company, building their entire reputations.

Many of these guys also continue to rely on their network for further opportunities and support. Their network would cut them out like gangrene, just like the old Enron titans, as to maintain their own good standing they couldn't be affiliated with somebody who clearly blew up their past company. That would be bad business, and that type of behavior would have prevented them from reaching those positions in the first place.