What Faramir says contains wisdom but so do Frodo's words. The enemy is trying to destroy the world with some kind of epic high fantasy apocalypse. Frodo does not terminally value the death (heh) of specific foot soldiers. They may be noble and virtuous and their deaths a tragic waste. But Frodo has something to protect and also has baddass allies who return from the (mostly) dead with a wardrobe change. But he doesn't have enough power to give himself a batman-like self-handicap of using non-lethal force. Killing those who get in his way (but lamenting the necessity) is the right thing for him to do and so yes, people would do well not to hinder him.