The first question you should be asking is, "why can moderators see who flags anything?"
There are some good arguments in favor of it:
- respond to flags and flaggers that require follow-up beyond what can be provided in a decline reason
- detect fraud and abuse ("revenge-flagging", attempting to automatically delete posts via the use of flags, etc.)
- access a user's flagging history to determine if they have a pattern of raising misguided flags
...and some good ones against it:
- conscious bias against users who raise a large number of flags (particularly borderline flags)
- unconscious bias against users with a history of being... troublesome... regardless of the actual merit of each individual flag
- potential for pushing users into more disruptive forms of interaction in a misguided hope of reducing flag quantity
Originally, moderators couldn't see who flagged anything! Over time, the availability of this information has been expanded as the need for it has increased, until the present day when comment flags are the only flags where this information is not provided. In regard to the pros / cons listed above:
- The vast majority of the time, flagged comments should be either deleted or the flag declined - extensive follow-up is a waste of time.
- We've had a couple instances of coordinated comment-flag-abuse, but it isn't common - and you actually can see who is responsible in these cases.
- There's no comment flag history available for anyone, so knowing who flagged wouldn't help you much there.
- Users are often prone to replying publicly (and starting fairly unconstructive flame-wars) - it's actually preferable if they flag instead, even if the flags are declined.