[quote=@TheMaster99]
<Snipped quote by UltikanaRe>

But that would require moderation, and would make filtering impossible. It's easier to have a broad list of tags, fit for most (if not all) circumstances while keeping the list manageable.
[/quote]

I honestly don't think it would require as much work as you think. A report system could be useful here (any word on that, [@Mahz]?), but simply have a list of banned terms (which would probably include sexually explicit content and whatever stupid things get reported) that cannot be made into tags. Filtering would work best with that auto-complete system that Mahz devised for Co-GM names, apply that same technology to tags and it would be possible to facilitate tag discovery without having to list out all tags, or do those silly tag maps or other awful things. Some popular tags could also be suggested, based on searches or newly-created RPs. 

These are all suggestions, however, but I think a custom-tag system is not too prohibitive.