The point is that the original question - as framed - was better served by saying "if you go back a step and reexamine your assumptions, you'll find there is a better path to your intended goal".
The new person has a different goal or a different set of constraints.
EDIT - which got me thinking. Maybe the "correct" thing to do is answer the original question as asked but gently point out to the person asking it that there is probably a better solution for them if only they had asked a different question.
The original question still stands and has an answer useful for other people. The original questioner has the opportunity to learn and ask the question they should have asked in the first place.
It's going to be annoying for someone - so it should at least be the person that kicked things off in the first place.
sometimes people who ask questions know the pitfalls but don't clarify that they know adequately because they are pressed for time. in this case those people unfortunately run the risk of being talked down to and they should accept that.
on the other hand if they have clarified adequately that they know what they're doing and they still want to do something that might seem weird then I agree it is disrespectful. Which is a thing you see often enough on StackOverflow to be notable.