your point about the "middle ground" between control and indifference is the point at which the defenders of the PD in its most extreme form lose the argument.
Because basically they're defense of it DEMANDS that they see no difference between intervention to help and domination or conquest. In the real world we'd recognize this as nonsense, but really to "defend" actions like in "Dear Doctor" leads one to poorly thought out arguments like either:
"giving them the cure is interference, and interference leads to conquest and subjugation!"
"giving them the cure would mean going around having to "help" civilizations everywhere in the galaxy, which would require such a drain on resources and time it would be unworkable!"
both are basically sloppy versions of the "slippery slope" and shouldn't really be taken seriously.
Help is not synonymous with imperialism, nor does it require crusading around the galaxy in an endless quest to right all the wrongs out there.
When you help the Valakans and not the Menk just because the Valakans have explicitly asked for help while the Menk are happy idiots (stupid housewives or Uncle Toms) you become something far worse than an imperial force. You don't merely conquer a world and subjugate its people, you randomly assist one group at the expense of another while being able to feel smug and righteous.
But go ahead, if you think that helping the Valakans is an ethical impetus helping every subjugated Klingon and Romulan species is a far stronger impetus. You'd have to go to war with each and every power in the two quadrants and you'd have to unleash a total war that costs billions or trillions of life.
Such nonsense, based upon intellectual laziness that refuses to acknowledge that you can't play in deep space like you play on Earth, should indeed not be taken seriously.