Well, my twopenn'orth...
The "who would you save in a fire" thing is completely misleading. In fact, there are a lot of ridiculous analogies being bandied around on this thread. The Tiktok not telling FFers that they are murderers comparison is ludicrous because giving a baby formula is unlikely to result in its death. It is a sad fact that the future of a sold puppy is much less certain.
The dogshouse topic has a lot of passionate people who have direct experience of the reality of irresponsible pet owners. Is it a surprise that they get angry when they frequently see death and pain as a result of poor decisions? A better comparison (although imperfect as we all disagree on the importance of an animal's life compared to a human's) would be this:
Imagine there were a group of people on MN who thought it was OK to treat children badly. Can't cope with your kids? Instead of seeking professional help, sell them, they can make you a decent profit! Such empassioned views against this would be acceptable, because the reality of doing such a thing is so abhorrent to the values of the average MNer. To the empassioned of the dogshouse (and indeed many others, who don't have the skills, experience and time that some devote to their advice on the topic), it is fundamentally important to reduce the risk of harm coming to animals, therefore when people ignore your (usually considered and lengthy) advice, it is terribly frustrating.
Instead of criticizing the posters who devote so much time to stopping the suffering of other beings, perhaps people should be informing themselves of the dark facts of animal rescue.
The original thread in question was a bit 
from the start. You care about your dogs yet won't consider rehoming them properly? Exactly what kind of advice do you want?
Personally, I rarely visit the dogshouse because a) I don't have, nor do I want a dog, and b) I get so upset, frustrated and angry about the amount of thoughtless idiots who think it is OK to risk the welfare of an animal purely because it isn't a human. Just because you would save your children first does not mean that animals deserve no care.
On a final note, you may not have intended this to be about one particular poster, but I bet she feels differently. If we agree with the "words on a screen" bullshit, this thread is void, as the poster of the selling-the-puppies thread could have just grinned and bore it.