I don't think I've encountered a labelled category for the counterpart -- the person who delivers information without receiving any in return.
I consider the "troll" to be a malignant subset of this category. Like someone who intrudes on another's conversation to interject a strong opinion in an offensive manner, then refuses to listen to any rebuttal or rebuke of their behavior, the troll interjects himself into the newsgroup's threads with no interest in gaining information (about either the topic or himself) in return. Instead, this is the sort of person who kicks over anthills just to watch the chaos he caused. His gratification comes from the attention he gets, not the contents of that attention.
Interesting...I've given nebulous thought to this topic, myself.
I consider the "troll" to be a malignant subset of this category. Like someone who intrudes on another's conversation to interject a strong opinion in an offensive manner, then refuses to listen to any rebuttal or rebuke of their behavior, the troll interjects himself into the newsgroup's threads with no interest in gaining information (about either the topic or himself) in return. Instead, this is the sort of person who kicks over anthills just to watch the chaos he caused. His gratification comes from the attention he gets, not the contents of that attention.