Many things are natural but bad. It is natural but bad to resent one's betters simply for the results of their talents, good fortune or effort. It is natural but bad to seek out those who may be oppressed and oppress them. It is natural, but impolite, to spit on the sidewalk. It is natural, but evil, to kill one's brother in raging jealousy.
That is why the argument that something is natural - or unnatural - carries little weight with me unless it is part of a larger and more sensitive argument. For example, that it is unnatural for old people's knees to flex to the point of fully kneeling is a perfectly sound argument for kneeling benches at the parish church.
