For example, I'm proposing a fraud detection system of my own design to address tricky issues in our product. Higher-ups want to purchase an existing system from a third party, which means I don't get to work on my pet project. They ask me for my input. At this point, my primary interest is in exposing all the flaws in their proposed system which render it unfit for purpose. I'll probably acknowledge some strengths just to make my argument more tolerable to them, but my goal is to persuade them to take my preferred course of action.
Likewise, if I rant about Java, it's probably because I would like to take some of the "mindshare" Java enjoys and move it to my favored language(s).
There are probably other reasons to want to damage something through criticism, but that's how I find myself employing it.
If some new idea or trend is painful or apparently harmful or even just mildly annoying then it's important to try to understand why and to articulate this in order to protect one's mental integrity. This can be done in private. If one is defending against the actions of another, it may or may not be necessary to communicate the criticism to that other person. Often it is sufficient to silently note why their actions are wrong. (And if one fails to accomplish this, perhaps the actions weren't bad after all. Thus a failed attempt at criticism has changed one's mind about something. This is useful and important.)
Sometimes the criticism must be communicated, perhaps even in the presence of witnesses. This can be hard.
Public criticism is a different matter. There one is trying to protect a subculture from some idea or work that one considers harmful. I'm not sure what are the proper conditions under which to give this or hear this kind of criticism. Perhaps one has the right to be heard only if one can advocate an alternative approach or artwork that is worthy of attention. Or if one has made significant personal contributions to the field.
Note that this comment is a criticism of criticism as it is generally understood and so it makes sense by its own terms. Most of us and most ideas have been the target of unjust criticism at one time or another.
If someone creates something and only gets feedback about what's wrong with it they could be lead to conclude the entire work is worthless and throw it out. However, if you say "this part right here, though, is great and for these reasons. Keep it and do more of that" you've actually helped someone's creative process a whole lot more than just "this sucks, get rid of it."
If anything it takes more critical thinking and analysis to point out what's good about something than just ripping apart what doesn't work. 100% negative feedback is about as helpful as someone telling you "Yeah, I liked the story. It had some spelling and grammar errors but other than that it was good!" Great, you didn't tell me at all what you liked about it but then continued to tell me what spell and grammar check already did.
I think words (or opinions or ideas or whatever you want to call it) don't hurt people. People are hurt by words. By this I mean that if and how much a person is hurt by a specific set of words is entirely subjective and may be controlled consciously.
If I stab two people in the neck, it's pretty much garanteed that I've caused them harm. Not exactly the same but probably similar harm. But with something I said I cause extreme distress in some person while it is completely insignificant to another.
I usually don't try to atribute malice to people. So I try not to believe critics (or anybody) intend to cause harm by saying what they say. But I don't deny some say extreme thing with the intent of causing a reaction or ever harming some set of people.
I tend to save my cruelty for those who have been actively trying to harm me. Which doesn't really happen, because I have a relatively placid life.
Interesting opinion. Criticism takes effort, something I am not willing to waste on those I don't consider worthy of my time. If I want to hurt someone, I ignore them. They get no feedback from me, no information on how to improve themselves.