Every time I hear this argument dragged out, all I can think of this - if there is someone who is so poorly trained/stupid/lazy that he will forget to off a safety, then why is that guy being given a firearm that is EASIER to shoot? If he sucks so bad with something simpler than turning the ignition of a car, then giving him a striker fired gun with a sub 6lb trigger is a ND waiting to happen.
And being from a generation whose image of a semi-auto was a 1911, I always find it funny when people trot out this trope. I went through Gunsite 250 in '87, and did a class with Chuck Taylor right before that. I also shot some USPSA/IPSC matches locally around that time. Pretty much everyone carried a 1911 and I cannot recall ever seeing someone forget to off a safety when it came time to fire. So I can't help but be amused at the gnashing and wailing of doods like this guy who dogmatically say it will get ya kilt. Maybe prior generations were just better? That is the only answer if this guy is speaking truth.