sear safeties

[STEINBVG]

I can somehow see a fearful point of those who insist on multiple layers of safety installed in guns.

Training or not, accidents happen even with the best.

But I would like to be able to see the point of the opposition to having safety devices installed, especially those a shooter can chose to not to engage.

For instance”perfect Glock” and I believe an elegant extra manual safety device called Siderlock.
What is a reasonable argument against having it on the gun?