Yeah I don't doubt it happens, but on the rare occasions I use PF, I look for what I'm interested in. Similarly, if I'm at the MB in Limsa I'm not reading chat unless it is from my FC.

I can see the sense in providing a toggle option that filters listings and chat that feature "18+" and "NSFW" as part of a more sophisticated block/self-exclusion function. But to answer the question posed in your OP, it is allowed because it does not violate ToS.