Don't you think there's a meaningful difference between a packaged, untampered-with Starbucks salad that was on the shelves just hours earlier, and a block of cheese from a stranger's refrigerator?
For the most part, I accept your point that old neighbor-cheese (and eggs and slightly-wilted vegetables and over-ripe fruit) is probably completely safe. But for better or worse, Americans just don't think about food this way. We have highly sanitized attitudes and expectations about food. I suspect this is largely because we are highly disconnected from the food manufacturing and chain of supply processes. We are uneducated about food, and as a result we throw it away if we have even the slightest concern that it is unsafe.
We have no problem using the same bacteria-infested, broken-bristled toothbrush for 6 months, but we have no qualms about throwing away a $9 block of gruyere if we detect the tiniest spot of mold. It's just how we are.