Why stop there? Buyers should ask themselves if they need or want anything at all. The responsible course of action would be to buy and use nothing—after all, we wouldn’t want to accidentally pollute more than all the fossil fuel industry or something.
You're right of course, but my point is that you can endlessly chastise people for buying things they do not strictly need under the guise of "not being wasteful" but it comes off as crotchety. Let people enjoy things.
Sadly we can't see that our want for fancy toys now will make food, clean water and shelter (a place to live not affected by heat, drought, flooding, forest fires, snowmageddon, etc) scarcer in the future.
It is a bit of a philosophical question: If the problem is our need for new toys, and stone-age style "bare necessities" living would perpetuate mankind indefinitely (or at least not cause extinction based on actions caused by mankind), would you want to live that kind of lifestyle and doom all future generations to that?
