Who's stopping him? Are we all required to be cheering him on for it too?

No one is stopping him, but they would be if the people in this comment section had their way. You are absolutely not required to cheer him on, and in fact you have the right to oppose him. But that isn't happening here. Nobody in these comments is exercising their first amendment rights to argue against any of his political opinions. They are using their first amendment rights to argue that the government should use its monopoly to restrict Gary Tan's right to make his argument at all.