It's easier to write a bad comment than a good one, so I don't think that downvoting bad comments should be more difficult than it is now. HN software already has little nudges that make it easier to gain karma than to lose it:

- You can earn points but never lose them by submitting URLs for discussion.

- You can't lose more than 4 points per post, no matter how many times it is downvoted. There is no upper limit to points gained from a single upvoted comment.

- There is only a 24 hour time window in which comments can be downvoted, but they can still be upvoted even months later.

The expertise problem is harder. Sometimes I see a post that has more misconceptions than sentences, but is grammatically correct and written in a confident tone. Only people who actually understand the subject matter will spot the problems quickly. It's tedious to write introductory level corrections for commonly repeated mistakes. For some of them I have considered keeping a mini-FAQ locally and pasting standard responses to standard misconceptions, but HN also discourages repeating identical posts.

If I downvote a misinformed post the original poster won't know where they went wrong, and people who see a grayed post won't necessarily understand what's wrong with it either. The saving grace of the downvote is that it affects comment sorting order, so at least misconception-heavy posts that are downvoted won't dominate the upper reaches of the discussion page.