Intensity isn't really the question, I'm thinking. Unless it's so intense that it's broken for anyone to have it, the question should be: is it somehow broken for a character class with poor Will save progression to have this ability, but not broken for a character class with a good Will save progression to have it?
If not, then why not allow the character with the poor Will save progression to "buy his way in" with the Iron Will feat?
(Again, I know nothing of the ability. If it's just plain broken, then it's just plain broken.)