It would have much more interesting to have episodes where their blatant Western colonialism had disasterous results BECAUSE of the contamination. It should be things like "The Omega Glory" and "Piece of the Action" that caused the Prime Directive - show me a disaster caused by interference, not a bunch or moral babbling about what ifs.
Yes, Ive been saying this for years. To fix "Dear Doctor" they should have provided the Valakians the means to create the cure. Phlox should not have the cure ready, it needs to be something that would take months to prepare, but Phlox can give them the instructions they need before the Enterprise leaves. Then in the middle of the next season the Enterprise finds out that the Valakians completely screwed it up, or worse tried to weaponize it, and both species on the planet were wiped out to extinction. If that's not a reason to create the Prime Directive nothing is.