Comment Locks

Moderators have the ability to prevent comments on any post. It's a great tool for some situations (such as when an argument in the comments is forming or has already broken out). However, from experience, it can also be disruptive:

• No explanation for downvotes/close votes. In fact, no feedback whatsoever. Comments are often the only viable way to get a post improved, since edits can often only be used when the original post is clear and the edit is changing something that's not too big (and would conflict with the author's intent) and not too small (low rep users must change 6 characters in a suggested edit). Answers are not for commenting
• No linking related posts
• Prevents review from working (Should a comment lock invalidate a reopen review?)
• Users find it confusing and frustrating when used on a new post

Due to the potential for abuse (namely for a user to try to prevent any criticism on their post), it's not something that should be given to everyone. I don't even really see a need for non-moderators to have it.

Your alternatives

As a regular user, you have two ways to help keep comments from getting out of control:

1. You can flag for a comment lock ("in need of moderator attention"). Most mods will only give you one if the comments look like they're going off the rails. Very rarely might a moderator use a lock because the question is on a controversial subject that tends to generate arguments (e.g. erotica). It's worth noting that moderators are already notified automatically when a post gets too chatty (i.e. 20 comments).
2. You can flag comments for removal. All users can do this under their own posts, but users with less than 15 rep would probably need to flag as "something else" and explain.