Whether it's pointless depends on the intended audience. Many online debates -- or for that matter, most in-person public debates -- are playing to the lurkers. Get both sides out there, and no matter which side (if either) a listener chooses, at least they know that no position is uncontroversial or axiomatic.
No matter what folks believe, I think they make better decisions and judgments if they've at least heard, and preferably considered, both (or more than two) sides. I'm not just playing devil's advocate -- I believe everything I wrote. But i also don't believe it's pointless to voice my opinion, even if there's a zero percent chance of convincing the person I'm addressing most directly.
Okay then, have at it.
You might want to try quoting The Jefferson Bible.