Advertisers that are now boycotting Facebook to protest "hate speech" have spent years running ads and marketing campaigns on a Russian social media platform that bans gay-rights groups and is known as a haven for white supremacists. Over 100 companies announced a boycott of Facebook last week in protest of divisive political speech on the website. The boycott coincides with a public pressure campaign led by Joe Biden and other top Democrats to press Facebook to enforce stricter control over President Trump’s postings. But many of these companies—including Coca-Cola, Pepsi, Adidas, and Reebok—have been regular advertisers on VK, a popular...