As a reader you typically don't know what the vote totals are and even with the vote totals they won't tell you anything about the quality or accuracy of the comment. I have not heard an idea about this "problem" which won't be a royal pain in the general case. I don't want to have to send people private messages when I vote. I don't want to have to write public messages when I vote. I don't want my access to positive or negative votes restricted because I'm not interesting in justifying my every action.

Generally I vote because I liked/disliked something, agreed/disagreed with, am annoyed with the person, am annoyed with the thread, am being deliberately contrary to someone's expectations (this is usually a -- vote for people who complain about -- voting), or most commonly am just exerting some control over the sorting of the nodes in the thread.

It appears you are responding to an imaginary complaint about downvoting. My complaint is about people who do not post corrections to others incorrect posts, instead they only downvote. Downvoting somebody for incorrect information does not help the community, b/c no one else can benefit from it, unless you are sorting by rep which as you've said 2/3 of the visitors can't do.

So downvote randomly if you feel like it, I don't care. But if you are going to downvote a node due to incorrect information, please post a comment.

No. I try to post correcting posts when I have the time and inclination. Often I prefer to just knock the node a bit. Maybe someone will notice that. Maybe it'll be sorted lower.