Does Starfleet have to stop other powers First Contact?

[yousirname]

Would Starfleet (hypothetically) have stopped the Vulcan landing upon the Earth in the movie First Contact? True, a small segment of the Human Race had achieved a single warp flight, but the vast majority of Humans alive on Earth were not a "warp drive culture."

My impression was that as soon as anyone in a particular civilisation discovers warp drive, that civilisation is regarded as 'on the map', so to speak. That pretty well signals that it'll only be a few short years before they're careening around the quadrant in their little tin cans, calling attention to themselves, possibly crossing the borders of hostile powers, etc, it's arguably necessary for their protection.

 

[T'Girl]

I've wondered in the past if Starfleet would shoot down human missionaries attempting to bring God to some poor unsuspecting pre-warp planet.

It's difficult to see why Starfleet would. If the prime directive indeed doesn't apply to non-Starfleet individuals, then there would not be any restrictions on sending out missions to various worlds, pre-warp as well as post-warp.

How often would civilians be on the frontier, away from the Federation's core worlds, or just away from warp-capable civilization in general?

The primitive (let's just use that word) planets are probably all around, wrapped around, the more advanced planets. Out of every 100 planets with intelligent lifeforms, maybe 99 are primitive.

So, it wouldn't be a matter of traveling away from the core systems. The primitive planets are intermixed with them.

Else the missionaries would have to explain how they're not gods, even though they appeared miraculously from thin air and even though they command other god-like powers ...

Native: You appeared out of mid air, are you gods?
Missionary: No, that's just how we travel long distances.

Native: Sister Kimiko cut her arm badly last badly and didn't die, is this magic?
Missionary: No, she washed it with soap. You get some animal fat from yesterday meal, I'll get some ashes, and I show you how to make soap. Later I'll show you how to make candles.

 

[Lt. Cheka Wey]

But if the human missionaries are civilians?

Can a human not be a member of the Federation?

I would assume that a lot of humans would end up as war refugees during the Dominion War. I don't see why not.