"There is a chaos, and then there is Chaos. One is the natural tendency of things to dissolve and become disordered over time, and must be maintained against. Sometimes it is beneficial, but that is a question for tech-priests, not Space Marines."

He pauses for a moment, "Chaos, on the other hand, is the forces of natural disorder writ large, supernatural, and built around uncontrolled and unbridled emotion that leads to corruption. Passion, in and of itself, is not a dangerous thing, but passion to the loss of reason is. Chaos is a representation of the various impulses and fears of humanity given form. Mostly commonly in the form of war, mindless blood-spilling daemons, though I've seen things of sickness and corruption as well, and heard tell of other sorts of corrupted... things."

As for the question of fear, he seems to be almost scowling.