I thought we could give barbarians another oportunity to use crimson mist, besides:
If they succeed the save, do they have an option as to wether or not they enter the crimson mist? Let's say the saving throw is provoqued by a demon or something nasty a character in their good sense would not face, specially if most of his companions are running away screaming. Could he choose not to enter the rage, and run away in his good sense? After all barbarians are survivors, not ravenous beasts that jump discriminately on whatever threatens them enough to force a save vs fear.
Fighting madness is restricted to certain races, so crimson mist is the prevalent ability of barbarians.