It's a feature up to a point, but it also introduces the problem of "compound reputation", where comments by those who have previously been heavily upvoted tend to attract upvotes regardless of merit. In particular, they tend to attract upvotes more than other comments by people who haven't yet established the same level of reputation on that forum, even if the latter comments are actually more helpful in that particular discussion.

I'm not aware of any discussion forum that has yet come up with an effective way to balance those competing effects. I suspect it would need a more complicated moderation/voting system that grades a comment on multiple scales independently, with credibility/correctness being one of them. But then you have a new problem of how to keep the system manageable so that users can still operate it with negligible effort and without the scoring system becoming confusing and more trouble than it's worth.