Pretty sure that the results haven't invariably been disastrous, but it does seem true to me that the results have been disastrous (or close to it) often enough for us to think very carefully about how (or whether) any such intervention should proceed.
Compared to what?
Was life all bright and shiny before civilization interjected itself into the existing barbarism?
I've generally considered the Prime Directive moral cowardice dressed up in self righteousness.
Was life all bright and shiny before civilization interjected itself into the existing barbarism?
In the Star Trek universe, frequently yes. Granted this is completely unrealistic sociology, but then again warp drive and the teleporters are completely unrealistic physics.
Disclaimer: I am not a philosopher, so this post will likely seem amateurish to the subject matter experts.
LW is big on consequentialism, utilitarianism and other quantifiable ethics one can potentially program into a computer to make it provably friendly. However, I posit that most of us intuitively use virtue ethics, and not deontology or consequentialism. In other words, when judging one's actions we intuitively value the person's motivations over the rules they follow or the consequences of said actions. We may reevaluate our judgment later, based on laws and/or actual or expected usefulness, but the initial impulse still remains, even if overridden. To quote Casimir de Montrond, "Mistrust first impulses; they are nearly always good" (the quote is usually misattributed to Talleyrand).
Some examples:
I am not sure how to classify religious fanaticism (or other bigotry), but it seems to require a heavy dose of virtue ethics (feeling righteous), in addition to following the (deontological) tenets of whichever belief, with some consequentialism (for the greater good) mixed in.
When I try to introspect my own moral decisions (like whether to tell the truth, or to cheat on a test, or to drive over the speed limit), I can usually find a grain of virtue ethics inside. It might be followed or overridden, sometimes habitually, but it is always there. Can you?