The DA/SA issue goes way back. Even before my time, and I'm pretty old.
The issue was that, first, the cocked hammer did create a hair trigger issue that led to unintended discharges, some of them tragic.
But second -- the part almost everyone misses -- was the credible-sounding false allegation of same .
That such a thing could be dangerous was easy for prosecutor or plaintiff's counsel to prove. In one case, the prosecution put into evidence the Colt revolver user's manual to show that cocking the hammer was forbidden unless you were going to fire immediately. One of the popular police training films of the '80s acted out an unintentional fatal due to the officer cocking his Model 10. Even if an officer had fired double action, the cocked gun argument was an easy hook on which to hang an unmeritorious plaintiff's action or prosecution.
This became so significant that in the late '60s/early '70s, LAPD rendered every service revolver on their department double action only. Miami did the same after the false allegation of cocked hammer case that @Glenn brought up, [I]Florida v. Luis Alvarez[I] between the shooting in '82 and the trial in '84. NYPD followed suit. Montreal did the same after the case that I think @HCM was referring to, Crown v. Allen Gossett.
We even saw the false allegation of cocked hammers in TDA autos. The only reason we see it less today is the dominance of striker fired pistols, which have their own issues if they have lighter than factory spec duty pull weights. See Santibanes v. Tomball and Galmon v. Phebus.
As some have noted here, opposing counsel can try anything and everything. The problem is, the "hair trigger" issue is extremely credible to a jury and difficult to refute. If they're trying to show arrogant recklessness with guns, being able to paint you as someone who thought he knew more about the gun than the company which made it or major departments which use it, proved to be a powerful tool for the other side. In a world where most PPC masters shoot revolvers double action from the 50 yard line, it's hard to convince a jury that single action capability was needed in a defense revolver.