MacArthur was not fired for wanting to convert Japan to Christianity; that is, he was not fired for working to send Christian missionaries to Japan to convert them to Christianity.
He was fired for strongly disagreeing with and disobeying Truman's wishes in the Korean war..
Conservatives supported Mac's idea of sending Christian missionaries to Japan. He did not get in trouble for that, but was supported.
MacArthur did not say anything about forced conversion, neither did Ann Coulter.
Liberals are the only ones who have said "forced conversion"