"Lackadaisical" has nothing to do with it.
An owner of a Glock once suffered a negligent discharge.Here's the rub:He ejected the mag, racked the slide, and nothing came out. Racking the slide again for safety purposes, nothing came out and he was satisfied all was well and depressed the trigger for field strip.
Why did he get a BANG that time? Because his extractor failed, and wasn't grabbing the chambered round when the slide was manually cycled.
He followed the "rules". He followed the steps. Gun still went bang when he didn't want it to.
In a world where 100% firearm safety can be established, then we can rely on our own wits. We don't live in a world where 100% of anything can be assured, except that Murphy's Law is 100% going to show up uninvited. Should Mr. Murphy pay me a visit, a manual safety is one more means of insuring his visit isn't a painful one.