Things flying into the engines of operating aircraft, especially during take-off and landing, is an extreme hazard that has been documented in many, many cases. Anything airborne poses a serious hazard to aircraft, even tiny particles of ash.

This is nothing at all like the threat posed by liquids. That's a response to binary explosives and is misguided at best. Powder mixtures can do just as much damage and they don't screen for those at all.