Smut and child porn aren't the same. Comparing the two is just as bad as saying that BDSM is comparable to rape.

I think what people are forgetting that not 'every' pm RP that is 18+ has sexy time in it. Some can be violence, drugs, other adult themes, horror, etc. It's a class for those that don't want an RP to be made public. Smut is just a class that draws a lot of attention because of legal repercussions if the person is below the age, as well as many other issues.

You could have an Erotica tag and if some selects it they get a message stating that erotica IC post must be made in PM, or something along those lines. Eventually the option of subscribing to a hidden PM thread might be a solution, but at least having something there as an indication or tag to the style of RP you want might help with some of the interest check confusion .