300 preaches against mysticism because it is one of the key enemies of logic, which is the foundation of freedom. Reverse-think if you have trouble getting it. Despite the movie, freedom can only be truly achieved, to the extent that we can enjoy it in reality, if one achieves free thought. Free thought can be achieved only if one's mind is founded in reason - aka logic. Mysticism, on the other hand, defies logic and demands that one pay homage to what cannot be explained, or understood, or believed. Throughout history, mysticism has been of the key weapons of tyrants of all color. Read Ayn Rand - she explains this far better than I ever can.