doctrinaire
adjective /ˌdɒktrɪˈneə(r)/
  /ˌdɑːktrɪˈner/
(disapproving)- strictly following a theory in all circumstances, even if there are practical problems or people disagree- a doctrinaire conservative
- doctrinaire attitudes/beliefs/policies
 Word Originearly 19th cent.: from French, from doctrine, from Latin doctrina ‘teaching, learning’, from doctor ‘teacher’, from docere ‘teach’.