They could do: but that puts the whole decision on mods, which for liability reasons I'd suggest avoiding.
Moderation should be reactive to complaints, not proactive... But that's just my opinion based on being part of a team moderating a site with 50k users where we had great fun with trademarked and copyrighted designs being allegedly infringed: proactive just didn't and couldn't work. This isn't quite the same, but it's somewhat similar
