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.
Imagine a pathologically idealistic, anti-religious, culturally-relativistic, iconoclastic, socially-irreverent, sociologically-progressive signature line here. Or don't.