In my opinion, the very nature of this website puts it at risk for, less than legal activities. By making the rules clear and obvious, they are simply making the intentions of the site known. This way, people who might break the rules cam't say, "What? That's a rule? Where does it say that on the site?" It's all about keeping the site, not clean, but ummm… I don't really think there is a word in the English language to describe the idea I'm thinking of.  Nevertheless, the rules are for the community's benefit. That's what I thank, anyway. I could be entirely wrong.