The inconsistancy is not necessarily between the back and the front, but the sheer stupidity of confiscating knives from passengers going through security and then handing them one once they get on the plane. "Would sir like a knife with a serrated edge or plain edge in order to hold the crew hostage and hijack the plane?"
Bit of a difference in the damage that can be caused between a cutlery knife and a folding pocket knife, especially some of the Swiss knives that have edges optimised for gutting (I know, I have one.)
However, the point about glass bottles is perfectly made - a broken bottle makes a fearsome weapon.