If right-wing terrorists are treated differently by the US government, it is probably because there are not large organizations of them, nor are there groups of them overseas that we can engage militarily. When there have been large, organized right-wing terror groups like The Order and the Aryan Nations, they’ve been vigorously investigated and shut down in accordance with normal law enforcement.
Taking the further step of outlawing free expression or infringing upon the freedom of association—even when truly reprehensible ideologies are at issue—is not a step that any Western government has taken for any other terrorist threat.