There are lots of reasons to argue with people online. One is to run through the arguments yourself with informed people and see how they stand up.

But in terms of persuasion, you're not likely to convince partisans to recant their heresy, so much as to make a convincing case that the uncommitted can buy into. A surprisingly large number of intelligent people watch online debates on social media, and people who are observing but not participating are much more persuadable. To that end, you have to be a decent, sympathetic interlocutor, who is personally appealing and has a good command of the facts and arguments. That means being fair, civil, honest, and straightforward.