When someone just responds 'LOL' to a post they disagree with, all it means is that they don't know how to say why they disagree. Either they can't think of evidence, or they just 'feel' they disagree with it. They'll usually try, when you confront them on it, to say that they thought the ridiculousness of the parent message was so obvious, all they had to do was laugh derisively. They may also say that they consider arguing pointless because of their audience, but this of course fails to explain why they laughed in the first place.
All in all, a single like 'LOL' response is the hallmark of what scientists have classified as a 'handsomehunk'.