Barbed wire is security theater. It was invented for cattle, and it does a reasonably good job of keeping cattle confined. (It doesn't work well for horses because horses are even more stupid than cattle and horses repeatedly injure themselves on it and the wounds get infected.)
Barbed wire doesn't work for humans, especially humans who have some familiarity with it.
Barbed wire worked well for human soldiers in WWI. It was part of a security system that also included trenches, artillery, machine guns, and active counterattacks, but it was a crucial part.
Barbed wire only slows you down.
Same with most locking mechanisms.
Oh definitely. That just makes it regular security, not security theater. (Again, assuming it's the "good" stuff from the military that you can't bypass quite so casually.)
I assume that means humans with adequate tools. If I didn't at least have some wire cutters or a carpet I don't know how I would get through it without grievous injury. (I further assume we're not talking about the serious barbed wire from WWI.)
In this case, they did it with a moving blanket -- just folded it over and tossed it over the barbed wire at the top of the fence, then scaled the fence. It was still laying over the fence then next day.
Barbed wire discourages casual trespassers.