There's a difference between being stupid and being dangerous. Both need to be educated.
The stupid and ignorant haven't worked out why their actions were stupid and ignorant and potentially dangerous. Having a word, or shouting, could lead to a few immediate reactions: immediate riposte, apology, silence, ignoring you, among others. But they may well take on board what they have done, think about it at a later time, and may become a better driver.
The dangerous know that what they are doing is bad and putting people in danger, and they don't give two hoots. I keep away from them in most instances. I say most, because sometimes winding them up in the right situation can be a lot of fun.
It reminds me of my football. People tell me to stop shouting at them. Now, I'm playing with people who have played the game for 30 or 40 years, and they have still not learnt some of the basics. Doing the wrong things badly requires someone to understand they are doing the wrong bloody things in the first place.
Probably because every one of their coaches or playing buddies thought that it was best to be nice and say "unlucky mate, better luck next time" instilled the thought processes in these people they were doing the right things. When they are not. And in a fast-paced football game, I don't have the time to take them by the hand and quietly and nicely tell them that they are doing the wrong fecking thing!
Doing the right things badly means you just need more practice, but at least you were trying to do the right thing. That gets applause and encouragement.
Same on the road.