The Philosopher's Riddle

Etched into this blade is a riddle that has been a matter of debate among philosophers for quite some time. Some say the pen is mightier, but I write my words in scarlet. This gilded quill does not use ink, and words can't change my course. In the right hands I protect the meek, while others carve a path in blood. What am I? Though many think the answer is simply the sword itself, a number of other solutions have been posited by high-minded thinkers and scholars throughout the years. What the actual answer is, none can say. The smith responsible for creating this beautiful weapon refused to spill their secrets that have since followed them to the grave.