If criticism is not to help but to hurt, isn't that called trolling?
Not necessarily. All of us, no matter how well intentioned in daily life, are prone to make criticism of people and ideas that we have no personal contact with. We generally are more careful and empathetic when being critical face to face. But, this here's the 'anonymous' internet and those of us who are more sensitive to conflict can find it harsher than usual.
and forum is built for differences of opinion.
Well it's a lot more than that. A meeting of minds, venting and a place of common interest. It's a microcosm of your world but with much sharper edges.
And most importantly say what you are criticising so the criticized might learn something.
That would seem self evident but.............people............ I guess on a forum like this most of us just bang down our immediate thoughts and don't ruminate too much on how it might be taken.
I've offended people in the past and have been horrified to find out that I had done so. I take more care these days to word things better.