There are reasonable assumptions and there are unreasonable assumptions. Naturalism (I’m not certain what you mean by “Darwinistic Materialism”) is a reasonable assumption. That a certain creation myth must be the true account of the origins of man, life, and the universe is an unreasonable assumption.
Why? For both claims.
Why is naturalism a reasonable assumption when there's simply no precedent for order, complexity, or life arising without an intelligence source?
Why is unreasonable to assume that order, complexity, and life have a intelligent source?