Are you really trying to defend all of the horrible things that the Marauders did to Snape because Snape (who had no friends or people to look out for him) retaliated in response? That''s saying if bullies pick on someone and then the person tries to fight back then they're all equally responsible.

And there is no evidence Snape ever used the levicorpus spell on someone to expose their underwear and humiliate them in front of everyone.