The thing about teaching that teachers need to remember (and I try to remind myself of this all the time) is that you're not teaching English or Math or History or really any specific subject. You are first and foremost teaching people. And people are unique, each and every one of them, so naturally, different people respond differently to different things.
There's no one-size-fits-all solution to problems that arise during the teaching and learning process, so saying that one way is inherently better than the other cannot be said. The most that can be said is "it depends", really. Every classroom is different and every student in that classroom is different, so the teacher needs to manoeuvre the people in the classroom the best way they can in order to achieve the learning objective, and ultimately, fulfil the students' potentials.
Having said that, there has been a trend in the education world that encourages and advocates positive reinforcement. Noticing, emphasising and encouraging the good things that the students do will in one way or another get students to behave in that way more often. Ignoring or not encouraging (which isn't the same as prohibiting) will get the students to behave that way less and less. The underlying assumption of this whole theory being that students want attention and have an inherent desire to be viewed as "good" in the eyes of other people, be it the teacher or their peers.
I would imagine that teachers who criticise students in a negative manner (condescending tone, degrading choice of words, all that jazz) still do have the students' best interests in mind and are doing so out of love. Who knows? I have this assumption that maybe they are trying to prepare the students for "the real world" that isn't as kind and considerate as some might think, and they're trying to strengthen their students' figurative jaws so that they can handle that figurative punch when it comes to them. Conditioning the students for emotional pain, in other words.
The issue I have with this is that while a student might be getting a lot of "conditioning" through emotional abuse, how many people in the students' lives actually take the effort to try to lift them up and help them believe in themselves and get them to go for their dreams and to never give up what they love? Sure you have your occasional "motivational speaker" to come in and spit a few lines for the kids, but how effective are they within that couple of hours, to be able to combat against a lifetime of denigration and the subtle instilling of the belief that they cannot, no matter how hard they tried?
Some tweets have said that the "garang" teachers were the ones that pushed them to become the people that they are, and I can attest that firm-footedness and high expectations have their place in the raising of young minds. But again we go back to the discussion of what certain students need, and how they differ between people. Those that thrived under their strict teachers, it could be that that's just the best condition for them personally to become better people and improve as students. But what about those that didn't thrive because of their teacher's garangness? What of the students that gave up on their studies because their teachers never once showed that they believed in them? How many people like that are around compared to the ones that have "made it"? And who says that those who "made it" could not have been better if only the teacher would have gave her or him an thumbs up every once in a while, just for encouragement? Who put that limit to their possible success?
Teachers don't have it easy, I'll tell you that.