Social Media Comments

Much of the posts about social media that I saw this week state that all comments that one posts should be positive because they lift the spirits of the one who posted what was commented on when they are going through a hard time. However, I think there are some cases where a negative comment might be warranted, when the poster is not known or seem to be in distress. These negative comments, to be helpful instead of hurtful, should state why they are not in agreement, focus on the topic or circumstances instead of attacking the poster, be respectful, not involve ranting, and be limited to misunderstandings of what people think or know about something or common knowledge and illegal acts that most people do not do. Do you think there are any legitimate reasons to comment negatively on something?