Facebook executives have long said artificial intelligence would address the company’s chronic problems keeping what it deems hate speech and excessive violence off its platforms. That future is farther away than those executives suggest, according to internal documents. Employees say Facebook removes only a sliver of the posts that violate its rules, and that Facebook’s AI can’t consistently identify first-person shooting videos, racist rants and even, in one notable episode, the difference between cockfighting and car crashes, according to the documents.