Seriously? "Why not just steal instead of helping to secure the network of a possibly world changing technology?" Are you that moronic?

Forget the moral problem everyone will have with your theft. If you steal a large block of bitcoins (assuming you get lucky on the first try) you have to liquidate them. Word gets out some guy got his wallet hacked by someone using an ASIC or whatever and hacking the keys to transfer the Bitcoins out and good luck selling your ill gotten gains. No one will want to buy bitcoins.