I have occassionally had the same thought/question as you do, JH. I think almost every person is going to suggest as Glockguy23 and Walt that an SA should be carried locked. I would add two more reasons: the SA trigger press is much shorter than the Glock making them slightly more suceptable to a negligent discharge than a Glock. Another reason for carrying locked is if your gun ends up in the BG's hand, you "may" have time to draw your backup or reacquire/fight for the gun if he doesn't know or think to disengage the safety. Though I can't cite specific reports, I have heard antedotal evidence of that scenario periodically occurring.
Having said that, I think you have a valid question. All mechanical safeties are liable to breakage. The most important safety is between your ears. If you obey rule three 100% of the time (finger off the trigger (out of the trigger guard and registered along the frame) until your sights are on target), you could "theoretically" carry condition 0 without a negligent discharge. But as Glockguy23 said, with proper practice, the safety will not add any time to your shooting.
Since condition 0 buys nothing in speed and yet provides more possibilities for a negligent discharge, condition 1 is the proper way to carry a SA. Besides, I feel good about the protocol when I am training or practicing on presentations, shooting, and status checks. It is just "cool" having to engage and disengage the safety, at least it is for me.
But then, I use the autoshift (manual shifting without a clutch) on my Dodge instead of putting the tranny in drive.
