Yes, they’re a threat.
Where do you think those boxcutters came from on 09/11? The hijackers didn’t carry them on. They were pre-positioned.
That's a really good point. I wonder if airport screening machines have an imaging log such that they could have gone back and looked at the images from when the terrorists went through. I've seen photos of them in security, but it would be very interesting to see what was on the screen when they were walking through. Or, maybe those machines were just metal detectors back then.