On top of knife amnesties and a punishment severe enough to deter it, you've got to do something to address why anyone feels the need to carry a knife, too.
And that means tackling gangs and other criminals, making communities safer, giving victims of crime a reasonable shot at justice.
I'm willing to bet that a large number of people who carry knives aren't like this bloke in Southport, they're people who for whatever reason feel they're in danger and that a knife is the best way to defend themselves. Properly effective policing would go a reasonable way in reducing that.
I don't know what you do about evil cunts who just want to hurt and kill people, though.
I refuse to believe that opening the doors of a dance studio during a class on a hot summer day is reckless or risk-taking behaviour. You absolutely should be able to do that.
If the perpetrator has a criminal record then you can argue there may have been opportunities missed to apply a deterrent or address whatever it is in his life or head that he thinks is reason to do this (don't ask me how you address it, I just don't know).
But maybe it's his first crime, or the first he's been arrested for. Especially at such a young age, it's not impossible.
Is there anything that teachers or social services might have been able to do? Does someone who commits atrocities show signs in childhood of who they'll become? Maybe, maybe not.
I don't know what the answer is. It seems to need a concerted effort from multiple agencies and even then you can't completely remove the risk.
One thing, though - this guy should never see the outside of prison for the rest of his life. For some crimes, rehabilitation is possible. Not this, though.