So here's a comparison for roleplaying and the way the forums could be operated.

Ever walked into a news agency? Sure you have. Magazines, newspapers, comics, all those random little trinkets to buy. Basically the guild is like a news agency and the different roleplays are the categories of magazines. Cars, fashion, holidays, business, computers... all these are like the genres of a roleplay.

Smut is an adult section. Special magazines wrapped in plastic that show all those naughty secrets and sexy ladies. Everyone knows it's there. There's nothing illegal about it. However selling to a minor is illegal without the proper identification. The magazine category is like the RP tags, the plastic wrap is the PM system, and the store clerk is the GM and Moderator. If they refuse to sell you the purchase, ie enter the roleplay, then you don't take off that plastic wrap and enter the PM of the Smut. If you can't enter the RP... then you will never know what's inside.

THAT is how you do an anology.

An analogy works best when it is compared to a neutral base. Adding a term like child porn will always start up an argument because it is a sensitive topic. There is nothing wrong with smut. Nothing... but there is something wrong with child porn.