Just to add, there is a lot of violence that could easily escalate to something deadly if the metal detectors weren't implemented. When I worked Mummy at HHN '08, we had at least one fight in our queue every 2 days, sometimes 2-3 a night. I had to hold two girls back from throwing each other in the ride track at port unload at Mummy for a couple of minutes while security ran up to get them. Though most fights happened in the dig site (the room where you go up the stairs to the load platform, with the hanging Anubis statue) and it's incredibly hard for security to get through there in a timely manner. I've seen tons of people escorted out with bloody faces and broken noses. And that's just at one attraction.
After the fight with the 2 females, I had to go down to processing and write a witness statement and explain what happened, and there was a LINE of people in handcuffs. Most was for fighting, but some were for stealing or trespassing. There's a lot of violence at HHN. I've seen it first hand on more occasions then I can count on both hands. I couldn't imagine what the outcome of some of these fights would've been if people could smuggle weapons into the park.