I've never seen a mechanical safety fail. I've seen a lot of people do dumb things in handling a firearm. If a person is afraid they will forget the safety is on in a critical moment they need more training.
Things happen. The firing pin broke on my Win. 1200 shotgun. When I chambered a round with the safety engaged, it went off. Several of us were standing in a circle loading when it happened, If it hadn't been pointed at the ground, it would have been bad.
I've had many pistols with decockers and used them, but I never trusted them to not fail someday. Mechanical things do break.