A person who stubbornly holds to his or her philosophy or opinion regardless of its feasibility
disapproval If you say that someone is doctrinaire or has a doctrinaire attitude, you disapprove of them because they have fixed principles which they try to force on other people. He is firm but not doctrinaire. = dogmatic. certain that your beliefs or opinions are correct and unwilling to change them
One who would apply to political or other practical concerns the abstract doctrines or the theories of his own philosophical system; a propounder of a new set of opinions; a dogmatic theorist