SAN FRANCISCO — Amazon quietly banned Adolf Hitler’s manifesto “Mein Kampf” late last week, part of its accelerating efforts to remove Nazi and other hate-filled material from its bookstore, before quickly reversing itself. The retailer, which controls the majority of the book market in the United States, is caught between two demands that cannot be reconciled. Amazon is under pressure to keep hate literature off its vast platform at a moment when extremist impulses seem on the rise. But the company does not want to be seen as the arbiter of what people are allowed to read, which is traditionally the hallmark of repressive regimes. Booksellers that sell on Amazon say the retailer has no coherent philosophy about what it decides to prohibit, and seems largely guided by public complaints. Over the last 18 months, it has dropped books by Nazis, the Nation of Islam and the American neo-Nazis David Duke and George Lincoln Rockwell. But it has also allowed many equally offensive books to continue to be sold.