Your argument suggests that people could still have the luxury of "preferences" in a setting like Auschwitz, and even exchange stuff that they didn't particularly like.

It's not like they served different courses for various tastes there...

The existence of trade is a strong indication that preference and choice was still available -- for why bother exchanging things otherwise.

I suggest reading the R. A. Radford paper that I linked in another answer, it's really fascinating.