I would just like to input a different point of view.
The whole concept of critical hits came from pen and paper RPGs and was meant to simulate hitting a vital area. It wasn't meant to simulate a "lucky" shot, at least not entirely. With modern day locational damage, the old school critical hit has lost some of its meaning: if I aim for the head, I do extra damage because the head is a vital location. But critical hits still serve a purpose: sure I can aim for the head, but if the opponent is wearing a helmet, I can't aim for a weak spot or opening, the game only knows I hit the head. That's where critical hits come in, they simulate you putting a bullet in the perfect spot. It's even worse with body shots, I can aim for the heart or kidney or liver, but the game doesn't register that. A sneak attack critical is a mechanic to say that, if they don't know you are there, you are much more likely to line up a shot on a critical area.
All that being said, I do think sneak attack criticals shouldn't do bonus damage on top of what a critical hit would already do. Until games are smart enough to truly register the exact location of damage and assess the importance of that location, critical hits still have a place, even sneak attack criticals.