On one hand, I think it's a valid criticism to say it's security theatre, to a degree. After 9/11, something had to be done, fast!, and we're still living with the after effects of that.

On the other hand: defence in depth. No security screening is perfect. Plastic guns can get through metal detectors but we still use them. Pat downs at nightclubs won't catch a razor blade concealed in someone's bra. We try to catch more common dangerous items with the knowledge that there's a long tail of things that could get through. There's nothing really new there, I don't think?

to nitpick, the 100ml rule doesn't come from 9/11 but from 2006 attack attempts