Given the environment malvolio was in, as an adult he still should be responsible for his actions. His intent towards olivia was never out of love but more of a struggle for social power. Although the fact that he was put to disgrace being treated like a madman for the sake of entertainment of other is not acceptable not even on today's society.
A clue to cause and effect would be the word "since" as it starts a cause for something,a reason for something to happen