Locke was acting like he did in the flashback to the therapy group. I think he had so totally believed in the living island, destiny scenario he had thought up to explain his miracle (and the miracle of their surviving the plane crash with only superficial injuries) that finding out the button-pushing might be a con reminded him of what his father did.

And this time, he was gonna get even. The island, or Dharma, wasn't going to get away with tricking him like his dad did. He was going to wreck their little experiment and laugh as he imagained all their faces when all the button-pushing-foolery stopped.

He wanted so much to believe. He believed his dad, twice, and lost his one true love (Helen).

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charlie98210
"Whoa!" she said. "Cry 'Havoc!' And let loose the dogs of war!"
And, like Banquo's ghost, they just won't go away.