Substack, the online platform that provides publishing and monetization tools for authors and writers, is facing pushback from a group of users who say it is giving a platform to Nazis and white supremacists. “From our perspective as Substack publishers, it is unfathomable that someone with a swastika avatar, who writes about ‘The Jewish question’ or who promotes Great Replacement Theory, could be given the tools to succeed on your platform,” the group of Substackers, led by writer Marisa Kabas, said in a letter to its founders. “And yet you’ve been unable to adequately explain your position.” The letter cited...