My brief daily tour of Facebook reveals, as normal, that a significant number of people appear to think that making assertions without any supporting evidence comprises a good discussion contribution.
If I read an assertion with no supporting evidence, these are the thoughts that immediately pop up in my head about the writer:
1. The writer is seeking affirmation, not discussion or discovery
2. The writer is lazy and/or uninformed
3. The writer has a fixed view on the subject and therefore believes that evidence and argument are irrelevant or superfluous.
4. The writer does not know how to discuss and debate, and is likely to be uninterested in learning
As you tell, none of those are exactly complimentary thoughts.
If (1) and (3) are true, then it is likely that the writer is not interested in a good-faith discussion. That is a contra-indication to my becoming involved in the first place. However, I may try to jog the writer out of their zone by asking them to provide some evidence to back up the assertions.
Good faith discussion is not difficult, but it does require some basic standards of behavior to be useful. Among those are extending the principle of charity by assuming that you are dealing with an open-minded person, not a close-minded idiot, and a willingness to actually process input instead of being emotionally aroused or triggered by it.
I have reached a point where I can tell within 2 or at most 3 exchanges whether a good-faith discussion is even possible. Quite often, working on the principle that life is too short etc. etc. if I determine that it is not, I walk away.
Walking away is an interesting action in itself, since it often shows how mature the other party is. If their response is “so you got nothing?” or “then I won”, (or, as in one recent case, an imperious demand of “why have you not responded to me?”) you know you are dealing with somebody who, to varying degrees, is behaving like a juvenile, or who believes that “winning” or being vindicated or validated is more important than learning. Since I don’t go into discussions to “win”, but to learn, responses like that tend to validate why I walked away.