Well, you're basically asking for the UN with teeth and without external oversight or control, so... yeah. Arguably one of the worst manners that could manifest, too, existing only to murder political opponents (maybe even ones that needed murdering, but we'd see how long that lasted :V) and nothing else.
Not sure I'd call it utopian, heh.
And nah, I wouldn't say so Helg. Those usually had to operate very much by the interests of whatever nation(s) they operated in, if perhaps not entirely.
And competence, don't forget the competence part.
Reasonably, I'd expect that with sufficient internal dedication to the higher ideals of the concept, as well as strictly practical matters, there's some chance it would be stably positive. Our hypothetical MSF is never getting to be big enough to go toe to toe with a major power, because they always lack the kind of base of support that'd allow it. No native population or industry to fall back on makes taking over the world difficult. A fancy island as a base of operations would actually be perfect for this, big enough to allow the MSF organizational room, not enough to let them conquer the world more than our scope of knocking over especially questionable conduct from other militaries.
Executive Actions did some pretty impressive things, but they were definitely caring about British interests throughout.
I mean, I'm looking at the Biafran War as my base of thought. The world was completely cool with letting Nigeria do some very horrible things because that served individual national interests during the Cold War. All they got were a few crazy mercenaries and idealist mercenaries, followed by Frederick Forsythe's afterword of "at least we tried."
World would be a better damn place in the long run if" at least we tried" was "we tried and we won."