To find and release publicly personal information about someone -- name, address, phone number, and even SSN and credit card numbers -- in such away that they become identifiable to just about anyone online.
It would not be legal (in general) in EU. Data Protection etc.
Yes, child porn is banned on reddit. But things that are protected free speech, but not child porn ("sexually suggestive images of minors") are also banned on reddit.
A term used to describe speech protected under the US Constitution / First Amendement, i.e. it's illegal for the government to ban this sort of speech (they can ban other sorts of speech). Reddit is based in USA, and learn close to the US legal definition of free speech (except in some cases).