This could also be an argument from the opposite side. In a dehumanising place only a market of self-interest survived. People only cared about themselves and would not share any food or other products unless they got something for it.
This argument suggests that everybody has the same preferences, which is ... a daring assumption. For example sharing your meat with a vegetarian isn't exactly useful.
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...
