In the Marvel movies Captain America and S.H.I.E.L.D. are opposed by the evil society HYDRA. Whenever a HYDRA agent is defeated or captured, they (almost) without fail chomp a suicide pill and utter the words 'Hail HYDRA!'
Why are HYDRA agents, both in WW2 and the present day, so uniquely committed to their organisation?
I am most interested in informed answers based on the movies, but supporting evidence from the comics will also be considered helpful.