What is the Point of Debating Online?

I came across this picture on FB that I think makes a very good point.  

Earlier this year, I was debating abortion with some people on my FB page and I was in several other debates on that topic over the period of a couple of months. During that time many people have said to me that we should just ignore pro-choice commenters, especially ones that are more emotional and do not give cogent arguments. They won't be convinced, so what's the point debating them? Not everybody says this, but it is something I hear relatively often.  Sometimes, you hear cynical people in any controversial discussion say "What is the point in arguing about this?!  No one is going to change their mind!"

I definitely understand that issue. It is very unlikely that they will be convinced by any arguments we give on this platform. In my experience, they often just repeat the same things over and over again without considering what my pro-life friends or I argue. I do, however, think that entering these debates with pro-choicers on FB is a worthwhile endeavor. I don't necessarily enter these debates to convince these people, though it would be nice if they were convinced. Here is why I engage them

1) It may at least help them understand why people are pro-life beyond "You just want to control women's bodies!"
2) It may help them become pro-life ten years from now.
3) It helps a brother out. If a friend of mine is debating the abortion issue with multiple people, I don't want to leave him alone. I want to help him out. I also appreciate it if people help me out and don't leave me alone.
4) I don't want these people to be so confident in their assertions. I don't want them to get away with saying what they want without being challenged.
5) The audience may be genuinely helped and educated by seeing your contribution to the debate.

I'm not saying that all pro-choicers are bad arguers or closed-minded. I am also not saying that there aren't legitimate times avoid engaging with some people. I just don't like the categorical charge that engaging them is always pointless because they won't be convinced.  This doesn't just go for the abortion debate.  This applies to any topic of debate online.