Tens of thousands of protesters paraded through Hong Kong on Sunday, waving placards denouncing “brainwashing” by China’s Communist Party and calling for the scrapping of plans for “national education” courses in local schools. The protest, organized by teachers, parents and student groups as well as local political organizations hostile to Beijing’s one-party system, demonstrated deep opposition to the introduction of classes that aim to boost knowledge of and attachment to China in this freewheeling former British colony of 7.2 million.