Crime on the tube

No, don't worry. Nothing bad has happened to me (yet). But a few months ago, they (i.e. Transport for London) started a campaign in order to fight knife crime on the tube, i.e. they randomly put up metal detectors on different tube stations. Today was the second time I've seen one in Stockwell. Apparently, the campaign has been successful, because crime related to knives has gone down (by as much as 30%, one of the papers states). But I'm still a bit doubtful about it all. It's absolutely fine that they just have a few metal detectors, and keep moving them around, but not everybody is searched, which is understandable, especially in rush hour traffic. However they target certain groups, which makes sense, but doesn't really improve relations with these groups of individuals. Also, every detector is watched/supervised by 14 coppers! Yes, fourteen! Ok, if they find something suspicious, it might be better to be more than one, or if a whole gang comes in, it's probably good to be a few people. But still!? Isn't 14 a bit of a waste of resources? Couldn't two of those policemen patrol the streets instead, or do something equally important?!