yes, we all hope it's been properly washed while at the restaurant, but it's not always the case, and we hope they use enough of the strong cleaning agent and disinfectant, but that's not always the case.
Oh, by the way, I still don't see what the big deal is, unless I misunderstand the double-dipping concept... You take a dorito for instance, dip it, bite off the dip and put the part that has barely touched your lips back in? Or you just lick it off and put the whole thing back in the dip? (cuz the latter is alot more gross
)