As an admin on another forum, we only allow the thread starter, and mods and admins to add tags to a thread. This way you always know who is tagging the threads and not everyone and their mom can tag a thread. Then if it is out of line it is easier for appropriate action to be taken.
Thanks for your tips for detecting the tag authors.
David would like forum users to add tags freely as long as they don't intend to violate TOS.
One of the benefits of leniency is to display forum users' behaviour.
It's very ironic to find out that Theo who started this thread himself added many abusive tags.