Trying to keep a certain level of civil discourse on a social website is not a slippery slope. Banning rape jokes is not a slippery slope. For as long as I can remember Facebook has had the option to report posts about:

- Hate speech or symbol

- Spam or scam

- Graphic violence

- Drug use

- Nudity or pornography

That is not trampling the First Amendment. There are plenty of other hate forums where people who are afraid of a slippery slope can freely enjoy and share rape jokes.