I doubt 'unflagging' is a relevant feeature to incorporate. The flag system is primarily designed to give an option for users to push threads into
the "ATS Headlines" since the theory is that discussion can be furthered encouraged by the increased attention based on the opinions of you the
user.
Flags are really only relevant in the first 24 hours of a thread; once 24 hours has passed the thread is not able to continue the headline
designation, making way for newer 'most flagged' threads...
I hope that makes sense...