Generally, no, because it disrupts continuity of threads to which you've contributed.
That's not a categorical imperative. If there's some extremely unusual case where deleting all posts is the Right Thing To Do, although I can't think of one, I'm sure the staff would consider it carefully. There have been a few unusual cases in the past that have been handled by less disruptive means than deleting someone's posting history.
“The egg hatched...” “...the egg hatched... and a hundred baby spiders came out...” (blade runner)
“Who are you?” “A friend. I'm here to prevent you from making a mistake.” “You have no idea what I'm doing here, friend.” “In specific terms, no, but I swore an oath to protect the world...” (continuum)
“It's a goal you won't understand until later. Your job is to make sure he doesn't achieve the goal.” (bsg)