It's because some overgeneralize, they have one bad experience and write the food off totally. Some foods are more risky than others when being added to a bin, either due to heating issues, potential ammonia, excess moisture, etc.. But the actual risk depends on other things like quantity, type of bin, how it's added, age of bin etc. as well as the added material itself. But some are still prone to be a bit dramatic and say food xxx is bad under any circumstance.

I have a 5lb bag of masa way out of date. How thick a layer did you add, or how did you mix it with what kind of bedding? I was a little hesitant to put much in.

I believe worms will eat ANYTHING that once lived, plant or animal...... Key is to feed slow and in moderation. Pocket feed to be safe.