Allowing force-push is considered an antipattern for Git, and generally best avoided. It's a safeguard against lost history and prevents data loss.
That aside, the comments are the history. Git is the wrong tool for the job. Why would you choose a generic version-control system designed for source code diffs & merges for the specialised task of chronologically-ordered comments? A database such as PostgreSQL is a far superior choice in just about every possible way. I admire your ingenuity here to make something out of what's available, but I respectfully disagree with this being a good way to capture user-generated content when there are better alternatives.