that is any member of the community's right, right?

If "right" means "thing it is technically possible for them to do" then it certainly is. If it means something more like "thing LWers are generally happy to see done", I think it probably isn't. I for one (1) would much prefer to be able to interpret the score attached to each comment as a measure of the LW community's opinion of that comment, which is badly broken when people do that, (2) don't make much use of total karma scores as a guide to a given LWer's general merit, and (3) would prefer a user's total karma score not to be strongly dependent on whether the people they've upset happen to be unscrupulous about breaking #1 for the sake of hurting that user's reputation. I think it unlikely that these preferences are very unusual.

The onus falls on the reader not to assign too much value to a comment or article's karmic value

Well, sure. But that's little reason for not trying to make the scores more meaningful rather than less.