One thing that makes "Homeward" a bad example is that by the time the Enterprise had arrived the planet was already pretty much dead. The entire atmosphere somehow turned toxic within a matter of hours. There's probably nothing they could have done away on such short notice. Whining about how Worf's brother saved some people was a bit over the top, but they can't be blamed for not saving the entire planet when they had no opportunity to do so.
It does, however, illustrate part of the reasoning behind the PD, although not in a very good way. Why did Worf's brother choose to save that particular village? Because he liked them better than he liked the next village over. Also because he was screwing one of the aliens, which is even worse. From a policy standpoint this is a horrible reason for interfering or as a basis of who you're going to save, especially when the observer shouldn't have been getting so connected in the first place.