Answer: doctrinaire

AnswerCrossword Clue
DOCTRINAIREImmovable
DOCTRINAIREAn impractical theorist or "rainbow chaser."
doctrinaire(French) a person who tries to apply principle without allowance for circumstance
doctrinairedogmatic about others' acceptance of one's ideas; fanatical.
doctrinaireSeeking to impose a doctrine in all circumstances without regard to practical considerations