Well, I won't go that far. I would say that a properly snugged metal-to-metal second stage connection is very secure and won't come undone with hand pressure. When you adjust your second stage (spinning to orient to your mouth), you want the "spin" to be in the hose, not where it screws onto the barrel of the regulator. A friction o-ring helps, but I doubt it would be AS secure and it would probably be a step backwards.
I use the friction o-ring for connections that are hand-tight only and cannot be snugged with a pair wrenches. For example, the connection the ADV or the O2 inlet on the head get hand screwed and unscrewed whenever the unit is put together. No wrench. Or, when you use an omni-swivel, which I've witnessed unscrew themselves from the second stage and pop off (fortunately on the boat).
The friction o-ring is a big help when the alternative is "hand tight metal to metal," but I'm also checking those connections all the time. Where I can snug up metal to metal with a pair of wrenches - as intended by the OEM -- that's what I do and have never had a problem.