To keep advertisers away from risky content, Facebook is turning off monetization for a few types of posts. It has published a new advertising guideline and a blog post, "Providing More Clarity and Control for Advertisers." In those, it outlines which types of content advertising can appear on.
Facebook isn't going to allow ads on fake news, on content that promotes illegal activity (i.e. drug use), or on adult content. It's also blocking monetization on articles about tragedies.
One of the most general restricted categories covers "fiercely debated social issues."
Content that is incendiary, inflammatory, demeaning or disparages people, groups, or causes is not eligible for ads. Content that features or promotes issues attacks on people or groups is generally not eligible for ads, even if in the context of news or awareness purposes, - Facebook