It would take quite the individual to stab someone in the chest with that knife. Then again a stick of butter in the chest would kill you "as surely as a bayonet". Of course only one of these is designed to stab someone.
By that logic everything can be used as a weapon and therefore banned or confiscated. That ^^ knife has had neither the tip filed nor the serrations sharpened. There is literally no point to your argument given that that ^^ knife is the one referenced in my comment. Sure it's possible that they may modify a generally harmless item to be deadly but it's not the case here for this instance. There was a movie that had a very similar theme to this call Minority Report where they arrested people people based on crimes they might commit. Lets not put our carts before the horses.
It would be substantially easier to kill someone with a hammer. Everytime they try to block a strike they take significant damage, if they're hit in the head it's all over. I think the police department that published this was mostly trying to let people know they're trying to pay attention and keep people safe... but honestly I don't see this as really demonstrating much of anything significant.
They went about it all wrong. They tried to play it like "Hey look we found a weapon, aren't we good at our jobs." When instead they should have played it like, " Hey look how good we're doing, a surprise search and this is all we could find."
*whispers* marmalade?