If you've got the glass ball that lets you see they don't turn into a world full of Reavers or Breen or Imperial space nazis, that can justify intervention, assuming you are willing to play God with history. But revealing the giant metal bird to them at an impressionable time is monstrous.
Kirk might be condemning them to millions of years of religious strife.
That's impossible to predict. The important thing is that they are alive
. They are an intelligent species - I see no reason not to trust them to work things out eventually.
One question, though: At one point, Kirk and McCoy are running from the aliens and Kirk suddenly slaps a tapestry with alien-looking writing on it, on a tree. Why does he do this? To slow the aliens down?