That's why I included a link to the review so you could refresh your memory.

But no, in that episode there isn't any conflict between the two races.
well, I remember not hating it.
the things is, even if they give them the cure - then what? sunshine and rainbows, everybody living happily ever after?
I always found it an interesting dilemma, because whatever you do would have consequences, nothing happens in a vacuum, including what precedence it would set from that point on. sure, the first impulse would be cure them no matter what, because that's the humane thing to do, but after all that's the impulse. no one thinks about what's gonna happen or wants to. would the federation have to help everyone now? to what extend? would that include military? and what if they say afterwards they not gonna help anyone anymore (because they simply can't), how would that work out?
if when there's a conflict between the species in the future, it means casualties that would never happen if nature would've run it's course. who knows if it goes to a point where they nuke their whole planet alongside it. "what if" might be fucking annoying but in that scenario it needs consideration.
point is no one knows what's gonna happen, so going with the most likely outcome you
can anticipate is the rational choice - even if that choice sucks complete balls. it's basically the trolley problem star trek constantly uses (including tuvix, which I also don't hate). even the crappy tng first season had an episode about unintended consequences for doing the "wrong" thing for the "right" reasons (s1e16, the one with the benjamin button admiral).
them being aware of it doesn't make it easier, and they probably could've gotten away with the cure if no one knows their involvement. but then my interpretation of the prime directive was always kinda a "ask for forgiveness later" thing. so you saved a civilization, did they see you? no? well, nothing to be done about it, move along... and if they saw you - enjoy your penal colony, you fucked up. reason we never saw the latter is because it's a tv series and they can't just demote picard or ship him off to some prison planet, so of course it always works out for a happy end. least that's one explanation for the one-sided display of it.