I don't suppose TSA staff are given comprehensive training on all things that are actually safe. I expect the training to focus, rightly, on things that could be unsafe.
They will also have extensive training on how it is their responsibility to use their judgement in preventing The Bad Guys finding new ways (shoes, fluids, who knows what) of getting harmful things into aircraft.
Before you insult a man walk a mile in his shoes. (That way when you DO insult him you'll be a mile AND you'll have his shoes)