Is it time to start calling out bad cyclists?

Depends what you want it to, or think it will, achieve. I recently cycled home without a front light having forgotten to move it from one bike to the other (I have 2 back lights for my 2 bikes because I am fancy). I was coming back from working at a cycling-safety event and wasn't entirely upset that no fellow cyclists called me out on it.
I don't recommend cycling without lights but in central London it's not the most dangerous thing you can do, as, I believe, statistics on collisions show. Added to other risky ways of cycling of course it will have more of an effect.
That's leaving aside the irony of people commenting on seeing cyclists who are riding without lights.

I've called out people this week who seem to be oblivious to how invisible they are. Usually people cycling very slowly on MTBs/Sit up and begs in South London on pretty big roads. I honestly think they don't know how dangerous they're being, but I suspect that for some of these people this is the least of their worries.
I'll also have a polite word with 'proper cyclists' who have low batteries, or, like a guy last night, had simply forgotten to turn his rear light on.

There's no need to be aggressive about it, but I think some people do need reminding about things that seem so obvious.