The tech giants have overthrown capitalism. That’s the argument of former Greek finance minister Yanis Varoufakis, who became famous trying to defend debt-laden Greece from its German creditors. Varoufakis has never quite regained the notoriety of 2015. But he has remained a prominent left-wing voice. After a failed campaign for a seat in the European Parliament in 2019, he plans to run again this June. This time, his adversary isn’t Berlin or the banks. It’s the tech companies he accuses of war...