Your argument assumes that the Prime Directive is an end unto itself, and takes it to a ridiculous extreme. The main purpose of Starfleet is to explore space and contact alien civilizations. The Prime Directive defines the limits under which they do that.
Anything taken to the extreme produces the opposite effect. If one takes the Prime Directive to an extreme that wasn't intended, then there'd be no Starfleet, because the Federation member races would all be extreme isolationists who never left their own planets.