Apart from being a health hazard to the user, I read it's illegal at least in some states in Australia as it can drift away and get breathed in by others.
Personally I thinking it is the paint residues that is the problem. Either way the paint residues are hazardous to begin with. The problem is the OEMs has found a paint that isn't hazardous in one way or the other.
My car was once covered by over spray from a shop next door. My black car had silver specks everywhere and I or anyone else could have breathed in the same thing.
As for my sand blaster I try to use crushed Walnut shells when things are too big to dine any other way.