It was hard to get into GLaDOS head and shut him down, it turned out that stealing Morality core, anger core and curiosity core was the key. Sadly, the way of defeating GLaDOS raised some serious questions.

Because they looked so human, they were all so Wheatley-ish... but he had t burn them all alive?

there had to be another way, surely?

Picking up the fairly heavy Morality core, who was blissfully silent, he looked at Wheatley and frowned. "Cores feel pain?"