When justifying themselves to parents, the argument given is usually that it's about safety. And we "just can't afford to take any chances." Defense against accusations of favoritism is also a huge factor, though it's not the one administrators generally blame.

There's a mailing list I'm on where ZT incidents are a common topic, and the explanation given by administrators is almost always that it's a safety issue. I can't recall the last time one of them said anything about preventing favoritism.

Back to the food issue, you're admitting that you're making a slippery slope argument. And I'm saying that argument is always bullshit. Thinking adults have to use their judgment. If they do, they'll see that some things are good, some are bad, and some are in-between. "Slippery slope" says you have to resist everything that is one inch away from your personal idea of truth or it leads to ultimate ruin. One problem is that everyone has their own idea of where "truth" lies, and will resist anything that doesn't line up perfectly.

It used to be called the domino theory. How'd Vietnam work for us?