I'm not sure that the Prime Directive is moraly correct. Who is to judge what criteria justifies intervention?
The idea is supposed to be that the natives of the planet in question are the ones with the right to decide their own fate -- that the Federation declines to impose its own will on the interaction. The problem with TNG's extremist take on the PD is that refusing even to allow the natives to know you exist can constitute denying them choice, making the decision for them, just as much as conquering them would. Especially the bit about "let them die rather than risk damaging their culture by letting them know we exist."
