Comment behavior can fall into a number of different categories.
1. Encouraged. Users get positive feedback for this type of behavior from community and/or moderators.
2. Discouraged. This type of behavior is allowed to happen, but discouraged through community norms or responses from moderators. This type of behavior may also be allowed to happen once or twice, but if it becomes a pattern, it becomes Against The Rules.
3. Actionable. Users exhibiting this kind of behavior will find some sort of sanctions coming their way directly from the moderators, not just from the community.