As any engineer knows, a MTBF (mean time between failure) analysis of any component in a device pre-supposes that component is both necessary and functional in said device's operation. Simply stated, the lock is neither functional in the normal operation nor necessary for that operation. Certainly, a catastrophic failure can occur... from a dropped firearm, for example. Sudden impact damage, from falls off counter heights to concrete floors, will cause damage to other firearm components, not to mention an accidental discharge possibility from a primer's cup being too high - or it's anvil being loose. Poor maintenance will rust through many items - with carbon steel going long before MIM parts. BTW, MIM parts are more durable - and much more uniform in construction (ie, less hand fitting required) - and definitely are a cost savings - as is SS!
But, when it is all over, it is a highly personal decision. I have had miserable luck with S&W's from the Bangor Punta era - SS or blued - and will avoid them. I have had miserable luck over the last three years with EVERY new Ruger - yet I still buy them (The generally can be fixed at my home... but my new 5.5" .45 SS Redhawk had to go 'home' for some r&r.). My new S&W's take a little break-in - replacement of the grips and springs for the 'fun' guns, PD types just get cleaned after the break-in. Again - buy what you want... but don't flatter yourself by thinking your promises to avoid lock-equipped will impress S&W to the point it effects a change. That little Spaniard on his burro, shouting at windmills, was more effective!
Highly opinionated...
Stainz
PS Ever found a real dud round? Do you still buy or reload ammo??