In addition to what you and the person you replied to already said, simply calling something stupid conveys very little information. "Stupid" provides no context, no rationale, and no direction towards improvement. If your goal is simply to push someone away, stop them from communicating entirely, or shame them, then yeah, dismissing a person's contributions as stupid is the tool for the job. But if you want better contributions and are trying to improve a project, you have to put in more effort than that.