@maxdancona,
maxdancona wrote: I am quite sure it actually benefits the stores.
I disagree with this part actually (after agreeing with parts of your previous posts).
There are several disadvantages for the stores that I can see. For one thing, I'm certain that I buy more when I'm hungry. (If I'm hungry and need to go food shopping, I purposely eat something at home first since the results of a too-hungry shopping trip can be expensive!)
Another has already been mentioned, that if you ingest something that is sold by weight, you can't pay for it (unless you're at Linkat's fancy newfangled store, that's cool).
A third is that if you're eating from a package -- so the price will be the same even if you have some -- that means
opening the package, which means that in the whole cart-to-conveyor-belt-to-bag process, it's much more likely to spill and create a mess.
I completely agree about mindless rules -- but this seems like a pretty mindful rule actually, from the stores' perspective.
If they don't give you a hard time about it, I think it's more "the customer is always right" than because it actually benefits them. (They tolerate it rather than encourage it.)
Which is pretty much my position too. It wouldn't upset me if I saw someone doing it (I never seem to) even though it's not something I do.