Problem is, they're such horrible marksmen that anyone could get hit (and they often do).
A few years ago, my brother and I were at an indoor shooting range in P.G. County, just outside of N.E. Washington D.C.
Several lanes over, there were three thugs, sharing a pistol. To say things like muzzle awareness was an alien concept to them, was a ridiculous understatement.
Eventually, one of them, holding the gun sideways, of course, managed to hit the return line. Not the one in his lane, either - IT WAS TWO LANES OVER!
Finally, the RSO came over and asked them to leave. Needless to say we never visited that range again.
I've seen movies of people holding the pistol sideways and tried it when I was out plinking and while with enough practice, you can shoot this way, it is not natural.
I doubt that even the super pros can become proficient with this technique, and I'd only use it in an emergency.