I think a lot of people need to be educated about what the benefits of debate are and how they manifest slowly over time.
Care to give any examples and the reasons for your first position and subsequent change?
I also liked to think analytically and enjoyed the intellectual stimulation I got from certain online forums (this one included). I liked how people would trade counterarguments and keep each other honest by pointing out bad thinking or logical fallacies. When someone would argue against something I believed in, I would argue back. From their perspective, my mind was not being changed and they were wasting their time, but from my perspective, the things they would call me out on stuck with me. I tried to avoid falling into logical fallacies and bad arguments because I knew I'd be called out on them. This restricted the ways I had to justify my beliefs, so that made it challenging. Then at church I noticed that nobody was being held to these standards at all, and fallacious reasoning was being let fly freely and constantly. I experienced a lot of cognitive dissonance during that point in my life which ultimately led to deeper investigation and study. I give a lot of credit to honest online debaters who pushed back on my ideas and kept me honest about the substance of my arguments.
The problem is when this wrong headedness starts to interfere at a public policy level, like climate change.
What I mean is, it doesn't even have to affect public policy to be bothersome. It also affects informal small-talk with acquaintances.
When people have clearly wrong beliefs (e.g. a square moon), it might not matter all that much to you, but they might harm someone else by spreading the trash, or worse, connect with like-minded people and create a real danger for others (legislate pi to be 3). That mind of trash is no less a part of your environment than the physical street, and I think it's a very good thing if you make an effort to pick up the trash, even if it's not yours.
And you learned the wrong thing. It is possible to change peoples minds and behavior with online conversation. It just isn't easy and it doesn't go quick (a single line directly pointing out a flaw often isn't enough, you have to bring across that you exerted effort, to show you care). If over time enough people invest time and effort into pointing out that you are wrong in something, you will change your mind. You might not admit it, you might not even notice it, but it will happen.
You might be right that it is perhaps not the fastest or most efficient approach, when you suggested spending time and money on actually influential things (though I'm not sure what you have in mind there).
Just look at the responses you have received so far here. Several people with different backgrounds have responded to you and said "you are wrong, you can change people's minds in online social interactions".
Now you have a choice. Will you hold on to your (really not very good for mankind as a whole) statement, so that it self-fulfills and you can still consider your own opinion correct and your thoughts and behavior consistent?
Or will you take that leap and believe people can change and act accordingly going forward?
Edit: I hope you realize that if you respond to my plea with a convincing statement and I believe you and change my mind, we both enter seriously troubled waters.
After all, do you really want to change my mind on the fact that one cannot change someone's mind in a social media setting, in a social media setting?
you could think the moon is square, doesn't bother me one bit. i'm living my life, not yours.
it's far better to focus on your own knowledge and self improvement. it yields a higher return on investment.
if you want to affect change, throw your time and money into actually influential things, not social media arguments.