The Prime Directive pisses me off. What defines "natural evolution?" We're all a part of nature. Just because I come from another planet and have more advanced technology than you doesn't mean I'm not natural! If a volcano threatens to wipe out all life on a planet and I have the means to stop it, not doing so would just be douchey.
agreed-the PD is stupid because the premise that an outside observer could judge what "natural evolution" would be for a group is ridiculous.