On the presumption that these are not all terrorists —
— which I presume because that would probably catch some headlines — then these people are idiots. I mean, I've railed at the, "Really, my little Swiss Army Knife keychain fob with the 3/4" blade?" kind of confiscation, and I occasionally forget to pull out my ziplok full of 3oz-or-less fluid bottles … but an inert grenade? A machete? Loaded guns (with one in the chamber)?
Anyone stupid enough to be carrying such an item and either forgetting about it or thinking it will clear TSA … is stupid enough that it should be confiscated and incur some hassle.
On the other hand … how many of those things were found via pornoscanner? #ddtb
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The TSA Blog: TSA Week in Review: Smooth Travel This Holiday Season – Plus Machetes Too!