Earlier quoted context omitted.
It's different if you own your own USB stick and only use that stick, and have the hosts configured correctly. Arbitrary USB devices picked up off the ground or provided by malicious people do terrify me, mainly because they can be keyboards or whatever in usb-stick physical packaging.
Even USB sticks that are your own USB sticks could be keyboards or whatever. Unless you've verified it isn't a store bought USB stick is just as risky as one that you picked up from the street or that someone gave you, in both cases you have no idea 'where it's been' before it got into your possession.
Things like the Bagram PX were concentrations of high value targets with only one source of supply. The general USB stick marketplace is a lot safer. In China they're often fake and thus unreliable (smaller than advertised), but in the US, I'd be pretty comfortable driving to a Best Buy 50 miles away and picking up a random USB token.
A USB key someone hands you is much more likely to be a targeted attack. A USB key randomly lying on the ground outside a target is also much more likely to be an attack.