I would never use all-black sights on a gun for carry or home defense. As we saw at
Southnarc's AMIS class, running around the dark without an aiming reference isn't cool.
That has been my experience when taking and teaching low-light shooting, as well. Blacked out sights are fine when you control the lighting... whether it's pitch black and you're using a flashlight or light enough to see. But the reality is that lighting is incredibly varied. Just look around the room you're in. There are areas of shadow, probably places where the light is harsh. You could be standing in one place and your target in another. Unlike most low-light training where the entire room/structure is equal lighting, you could move from bright to dim to dark and back many times.
The easiest example is a backlit threat. If you're in a position of darkness and the threat is heavily backlit (a strong light behind him), all you'll see is a silhouette. Try aiming at a giant black silhouette with black-on-black sights. Here's a perfect example of an identified threat that you can shoot without turning on your light, but you've got no aiming reference. Even students running
only a front tritium dot with black rear sights have a lot of trouble with that shooting problem.
I was playing around with my new sights -- the first 3-dot night sights I've used in years -- just walking around my house "engaging" various objects. There were plenty of times where I found myself in a dark enough position that my tritium sights were visible while engaging a dark-colored object that would have been very hard to aim at without those glowing dots.
The recent trend in some circles towards plain black sights originated with military folks who are used to operating in a team environment where everyone has lights on their weapons 24/7. A team kicking down a door or blowing a hole in a wall to enter a room isn't as concerned about giving away its position once the action starts as Harry Homeowner might be.
There's absolutely no question that tritium sights help people shoot better in reduced lighting. LE agencies have proven that beyond a doubt for decades now. We also know that the typical civilian or law enforcement violent encounter in the U.S. has a strong possibility of occurring under conditions of reduced lighting. It's not hard to draw a conclusion from that...