And no, they didn't "request assistance." That's more of that condescending, White Man's Burden thinking, the reflexive interpretation of other cultures as needy and dependent on your superior benevolence. What they did was to seek knowledge. They wanted to learn more about the universe. But sometimes the worst thing you can do for someone seeking to learn is to just hand them the answers. Then they won't develop, or retain, the skills to learn those answers for themselves. And who's to say they won't find new answers that never occurred to us? Again, just because something is our way doesn't make it the only possible right way.
Using myself as an example, I've taught people how to play the Piano.
I've had students that start from scratch completely, and pick up the lessons really quickly, that I find myself getting into more advanced concepts with them really quickly. I had a kid who was playing simple chord progressions in about a month's time, and within 3 months he was a really good beginner.
Other students have taken much longer to understand basic concept, and I have to really bring it down to basic steps for them.
Anyway, the bottom line is that there's knowledge that is pretty much absolute. The table of the elements for one. Unless someone comes up with a radically different new theory on the atomic weight and composition of elements that makes even more
sense than what we know now, then I think it's safe to assume that our current knowledge is pretty accurate, and would not change on another planet.
This type of foundational knowledge could have been provided to them and I don't believe it would cause any serious repercussions.
Their leader already knows of incredible materials of construction, to build vehicles that can fly far above her world. While they probably knew their world was round, it's unlikely anyone could have imagined what it looked like from that high up. Now at least one person knows. This person also knows of incredible technology that can make you disappear and reappear in another location. And a bunch of people know that it is possible to make things invisible and create fake camouflage, like a realistic looking mountain edge.
At that point I don't see how just leaving makes things any better.
The episode takes Evolution to the level of a religion, and to say let nature take its course is just another way to say its God's Will the Valakians die. Phlox had no business working on a cure, then, whatever happened to the Menk if he's going to be consistent. As for the Menk and Valakians living together, they'd been managing it up to that point. Who's he to decide they can't do so in the future, since by withholding the cure that is what he has done. It is everything reprehensible about the Prime Directive from TNG on in Trek.
Enterprise was pretty schizophrenic on the whole "interfering with other cultures" idea. It wanted to tell us it was right, while looking like it was wrong.
TOS told us it was wrong while looking like it was right.
TNG just flat out said wrong, with no leeway.