It's not just you that they're worried could get stabbed, it could be anyone.

I took some psych courses in University and one of my profs was full of anecdotes about patients he'd cared for, there were people who were perfectly nice and calm and then in a split second something would go unpredictably wrong and they'd be savagely attacking whoever they could get their hands on.

And then a moment later they'd be beside themselves with dismay over having "lost it", apologizing sincerely and profusely. He said it was really hard keeping on your toes in there. He permanently lost his hearing in one ear when one of his patients slapped him out of the blue one time, to both of their surprise. If anything remotely like a weapon was easily accessible it could go very badly.

I'm sorry your experience was unpleasant, and of course I can't remotely speak to it myself - it was your experience, not mine. But it could be that the stuff that was done was for everyone's protection.