Some time in the later years of the revolver era, NYPD required its revolvers to be converted to DA only, after a patrolman cocked a Model 10 pointed at an unarmed suspect and then touched off a round unintentionally wth fatal results. I think that there was a similar LAPD policy at some point too.
I doubt that either or any department ever trained officers to cock their revolvers while holding suspects at gunpoint.
But officers are people too, who grow up watching the same crappy movies and cop shows where actors cock their revolvers (and when technically possible pistols) all the time to enhance their threatening appearance or reinforce orders. And under stress people have a tendency to revert subconsciously to stuff like that.
I wouldn't worry about lawyers, I'd worry about killing someone. If you think you might start cocking the hammer in a stress situation even though you know that's a dumb thing to do, maybe because you practice a lot of single-action target shooting, removing that possibility from your primary defense gun might not be a bad idea.