Comments are also a way for the community to get involved in discussing an issue. That way, they will feel like they are part of the solution to a particular problem, which facilitates joining forces for a particular cause.
Basically, a blog is a great advocacy tool, because it allows anyone with an internet connection to launch a campaign for social change. It empowers ordinary citizens to oppose authorities, to act as alternative sources of information, to organize supporters, and to lobby those in power.