TOS Starfleet probably would have reinforced the border and let the Klingons kill each other.I have my doubts whether the PD of Kirk's era would have prevented Starfleet involvement in the Klingon Civil War for instance...
Like when the Arabs gave the Europeans mathematics, silly idea.i think humans realized it made sense because of the disasters on Earth with less advanced cultures.
It's a question of do you accept that there will be bad mixed in with the good, or do you withhold the good to prevent the inclusion of the bad.
If you remember the episode, when Kirk did try to do exactly what you're suggesting, Vaal wouldn't allow the landing party to beam up.I mean once they got their asses kicked they should have cut their losses and got the hell out of there