I'd find that a more convincing argument if there were clearer guidelines about what the security guards can and cannot confiscate. But yes, anyone who tries to take a SAK or a Leatherman through security these days would probably have no legal recourse if the guards refused to return it. If it's something that's "permitted" by the official guidelines (like a round-tipped butter knife) but the guards decide they don't want to let you take it through, I'd expect them to give you the option.

I suspect, like anything else, it's pretty much up to the individual guard - and probably more than a little influenced by whether or not you addressed them as "jack-booted Storm Troopers" <img src="images/graemlins/wink.gif" alt="" />