No matter how clearly labeled, common-sense, or standard practice something is, people will always find a way to rationalize not knowing or push their dislike of it on to someone else, usually an undeserving person. It is a simple lack of personal accountability, and happens everywhere.

I worked for years at a bar, the number of people who tried get more scotch put in the glass when they ordered it neat (no ice), because it didn't look as full as their friend's on-the-rocks was astonishing (poured via shot glass, simple displacement effects here). These were ph.d level people who should know better. Of course the on-the-rocks people tended to complain about it tasting "watered down"... sigh.

Anyway, there is a highly amusing website: http://notalwaysright.com/ that will probably provide insight into this phenomenon. I believe most of those stories have happened, having witnessed most of the scenarios (albeit with my own customers...)

Point being, excusing people for not noticing the big rating that is on the front of the box is probably the wrong answer, at some point we have to accept that someone needs to be responsible. Otherwise, we just keep passing the buck, I mean how long until we can just claim "oh I didn't understand the rules for labeling, it is obviously too much to expect me to read all those rules, we need a better rule system from $oversight_org", and then the org says, "oversight is too hard, how were we supposed to know that those naked people actually meant nudity"... and on and on