I recently unfriended someone on Facebook who I had been friends with online for years. We hadn't met in person, but we'd exchanged a fair amount of comments and a few messages, and I liked her as much as I knew her, and still do actually.
We'd also had a few differences of opinion at times that occasionally got a bit contentious, without turning into full-on arguments. Actually we had a lot of differences of opinion. But mostly it was a matter of her posting views I disagreed with to some extent, me reading them and usually not commenting because I knew it would likely lead to an argument. It wasn't so much her positions I disagreed with as it was her tone and her approach to solving the problems she would bring up.