Shows like this, like ST:TNG, were edited on tape using the interlaced frame rate. So it's not just that it was telecined for airing; the complete episode never existed in 23.976 fps form.
I'm not sure if I understand what you mean about fades, but dissolves between two shots are one of the problems with this type of content. Because they took footage that was already telecined and edited it together, you end up with dissolves between shots with two different pulldown cadences. The result is that no combination of fields lines up to produce a full frame, requiring actual deinterlacing for those frames.
You can force the square peg into the round hole, but not perfectly, and not even well using the solutions available on Mac. Avisynth is needed for such wizardry.
Modern graphics cards recognize and reverse pulldown during playback as part of their deinterlacing engine, the same way TVs do.
You can't change a variable frame rate video to constant frame rate just by telling it to play at a certain speed, because then the frames that are supposed to be shown for a short period of time are onscreen longer: you lose audio sync.