But pretty easy to cause blunt force trauma to the head

Generations of Native Americans beg to differ.

The native-american generations population probably doesn't intersect with the population of teenage knife-wielding attackers in london, which is what we're talking about.

Then again, if you want to argue stone-age semantics: we can't ban anything and should just resort to continuous murder since rule-based society is too hard.

We just need to watch out for teenagers learning flint-knapping.