If the people are participating in social media forums where debate happens or can happen (without it being considered rude), then they have not yet fully enclosed themselves into a comfortable echo chamber. If they aren't just there to troll, and seem to be engaging honestly, then debating with them is not a waste of time. Nobody is going to change their mind to match yours during one single online discussion (unless they come in wanting to have their minds changed and experience a lot of social pressure to admit to it, a la /r/changemyview). The audience matters, and even the person you're arguing with will likely remember the points you made, even if only to counter them, the next time they voice their opinion. The same goes for us. We learn more about their side and where they're coming from each time, and that counts for something.