Discourse and dialogue on certain topics should be encouraged where the alternative might have been none at all. The information age has helped make more issues visible to society in this way. (If we go about it respectfully).
It allows anonymous conversation to take place with people from a multitude of backgrounds to expand our world view and potentially change our viewpoints of topics.
It's just as useful as arguing IRL. Some people might not take your arguments into consideration anyway. Arguing is a great thing, but just with the right people.