"Really, I kind of get tired of reading stuff like this because there is always some subtext to it. "mean-spirited" usually means, "someone disagreed with me"."

Unfortunately this is often the case, however it should still be possible to make some sort of judgment based on rationality, patience, and communication skills of the people involved in a debate. If one side is constantly irrational and/or impatient then they are often also described as mean-spirited. This is why comments/complaints like the op's can be valid and important; though (ir)rationality/(im)patient/lacking communication skills are my preferred terminology over "mean-spirted" and other similar descriptions.