He didn't take anyone's money..... He played a bad prank and lost a lot of respect.....
He took advantage of his "bet" to dump his Pirate's debt while pumping up the price. So it's a double scam.
How so? No money changed hands as a result of MNW's bet, (other than the example 20BTC) so technically he hasn't stolen anything from anyone... UNLIKE the multiple ponzi schemes and fake exchange hacks. If MNW didn't actually take anyone's BTC up front, how did he "dump his Pirate's debt"?
Because with his "bet" he slowed the rate of decrease of the price of (phucked) Pirate's debt, just enough for him to sell the amount he owned with minimum loss for him and maximum loss for who took his words as serious. Clear enough? It's called "pump and dump".