Worth pointing out that you're talking purely from a US point of view, and different countries treat slander and libel differently.

For example in the US, to sue for defamation you need to prove something is false, whereas in the UK the defendant has to prove that what they said or wrote (and are being sued for) is true.

(I've no idea whether this app had any non-US use, but thought worth adding this comment regardless since it's a general point about defamation law and being discussed on a site with a big international audience.)