Now, if you have the habit of reading through someone's comments all at one time and judge each comment for its own value

No, that's not what I have been contemplating.

"A commenter's karma means nothing," is a bit of an overstatement because you need 20 karma to post. Also, most commenters are probably aware of changes in their karma. And if I reduce a person's karma by 20 or 30 points, I would send him a private message to explain.

What I propose reduces the informativeness of a comment's point score but more-or-less maintains the informativeness of a commenter's karma. If enough voters come to do what I contemplate doing or if enough well-regard participants announce their intention to do what I contempate doing, then the maintainers of the site will adjust to the reduction in the informativeness of a comment's point score by focusing more of their site-improvement efforts on a commenter's karma. Note that those site-improvement efforts will tend to make effective use of the information created by the voters who follow the original policy of voting on individual comments (as well as the information created by voters who vote that way I contempate voting).