I took it that these sort of situations have occurred many times to the crew in the past, and they figured there was no point in getting all weepy or strung-out over it and just deal with it as usual.
That's really not the issue here, and I apologise If I've not expressed my objection to this episode clearly.
I fully agree with you,
Anwar, when you say there can be circumstances when acting to save a pre warp civilisation could be impractical. I'm even willing to accept that there may have been nothing the Enterprise crew could do to help in the episode Homeward.
What offends me, truly offends me, about this episode is that the crew, the heroes, are unwilling to even discuss the possibility of saving them. They apparently believe that total extinction is preferable to 'cultural contamination'. Instead of the hopeful, optimistic view of the future we normally get in Trek, here we have a cynical, jaded version.
I can't remember if it was this episode or not, but I recall a Picard speech about how the PD is intended to protect Star Fleet from making such decisions. So rather than an attempt to help pre-warp cultures, it has suddenly become selfish.