We insist on eating hot food to show we are not tzdukim. Maybe same applies to eruv?
One interesting argument I see in this discussion – if some shita is constructed in a way that invalidates all eruvin (or, if I can expand – invalidates what was normal practice before) – then it is apikoirosus, not chumras. Thus, if there is a kosher eruv, one must carry. There is probably a loner list of activities that one must similary do because of people asurim what used to be matir. I’ll leave it to others to suggest them.