Twitter's newly minted owner, the self-described “free speech absolutist” Elon Musk, is about to get a crash course on global content moderation. Among his first moves after completing his $44 billion takeover Thursday was to fire the social media platform's top executives, including the woman in charge of trust and safety at the platform, Vijaya Gadde. He also posted a conciliatory note to wary advertisers, assuring them he won't allow Twitter to devolve into a “free-for-all hellscape.” The problem is, not even the world's richest man can have it both ways. Lightly moderated “free speech” sites such as Gab and...