Destructive criticism
People strive to give their input usually because they see something is wrong or can be improved — that's criticism.
However, for it to be constructive, a great deal of effort must be made: both empathy and humility are required in order for the criticism to be constructive. On top of that, it also must be timed right, since it is a well known fact that the right thing in the wrong place (or in this case–time) can make a huge difference on the appearance of said criticism.
So it is in fact very not trivial, to provide constructive criticism. And if any of the aforementioned prerequisites are not met we end up with destructive criticism.