That's all true, but I'm not sure that's relevant. I agree with the GP, not because my posts are downvoted, but because I see respectful, thoughtful posts from established users of reasonable karma downvoted into greyed-out territory for no obvious reason other than that their opinions (or their facts) are not popular. This includes posts I agree and disagree with, so I don't think it's necessarily bias. I also think it is behavior that has become endemic (although I may think so because I find myself having trouble not doing that).
Introspecting into the occasions when I myself downvote out of disagreement it is usually:
1. I think the other person "doesn't get it."
2. I lack the time to offer a substantive opinion.
3. The other party has demonstrated either: a. A tendency to view statements ungenerously or; b. that they already know The One True Way.
Y'all may wish to evaluate whether #2 has an undertone of 'instead of accepting their argument', as we human beings have a latent tendency to find the easiest way to reject contradiction. I think that the below thought process, whether conscious or unconscious, is affecting downvoting behavior on most online forums that permit unmoderated downvotes:
"I'm confident that I'm right and they're wrong, but their argument is very well put, and after a minute of thinking about it I can't find any way to contradict their viewpoint. I'll just downvote it now so that I can mentally dismiss it and move on without giving it further consideration, because otherwise it'll continue bothering me that I might be wrong."
(And, to parent: thank you for taking the time to reason through this and consider your own actions. I'm not sure where I stand on #1 at all. I'll have to think on it a while longer than a day.)
Introspecting into the occasions when I myself downvote out of disagreement it is usually:
1. I think the other person "doesn't get it."
2. I lack the time to offer a substantive opinion.
3. The other party has demonstrated either: a. A tendency to view statements ungenerously or; b. that they already know The One True Way.
4. Some combination of the above.
Edit: List formatting.