You seem to imply that weapons with BFAs fitted are still firing real rounds, which are rendered safe by hitting the adapter. That’s not true. They are firing blanks, which are cartridges with the bullet and some of the powder removed. Pull the trigger, you get a pop, a flash, and some smoke.
They aren’t wrong though. There’s different types of “blanks”. There are blanks which are completely “blank”, but there are also “blanks” which just have a regular shaped bullet, but a very light one, made out of balsa wood, and those do require a blank-firing adapter and while they wouldn’t fly far from the barrel, you could hurt someone with one probably, but more importantly the blank-firing adapter also restricts the gases which are let out, thus increasing the (otherwise inadequate) pressure on the reload mechanism, so you don’t have to manually reload. In fact, we here in Finland call it “sysäyksenvahvistin”, and the direct translation wouldn’t be “blank-firing adapter”, but “increaser-of-pushback-pressure”, more or less.
It’s easier to make blanks like that than it is to make ones which don’t expel anything and still manage to keep a semi- or fullauto reloading.
There’s a mandated 50m safety distance for these, but I once got shot in the face from less than a metre a way while we were practicing urban warfare. I was spitting balsa wood for the rest of the day.
One dipshit ones had blanks in his mag, didn’t have his safety on, didn’t have his blank-firing adapter installed, and the gun was fucking loaded. Sure it probably wouldn’t have killed anyone, but that shit was still dangerous.
Soooo yeah, it is exactly what certain types of blank-firing adapters do.