User blog comment:ProfessorKilroy/Sony Announces "Venom" & "Sinister Six" Films/@comment-4651179-20131213183338/@comment-4651179-20131214234319

He put on the suit because he was angry and indignant because a "mutant" not only destroyed that project but also because he stated it couldn't be controlled. The usual "do the opposite you're told." The suit increased that anger, which led to Venom trying to kill Peter.