What's interesting to me here is the extent to which commitment to rationality is linked to a belief in moral objectivity. A believer in objective morality can argue that everyone ought to do one's best to believe what is true, even when believing the truth is emotionally costly. Whatever is legitimate in the Outsider Test for Faith appeals to this kind of commitment. But does this commitment make sense if moral relativism or moral subjectivism is presupposed?
Bertrand Russell wrote, concerning fideistic believers:
There is something pusillanimous and sniveling about this point of view, that makes me scarcely able to consider it with patience. To refuse to face facts merely because they are unpleasant is considered the mark of a weak character, except in the sphere of religion. I do not see how it can be ignoble to yield to the tyranny of fear in all terrestrial matters, but noble and virtuous to do the same things where God and the future life are concerned.
But, if there's nothing objective about moral values, then there's no objective reason why I shouldn't be "pusillanimous and sniveling" if it keeps me emotionally comfortable. The appeal to intellectual honesty presupposes a commitment to the value of truth, which is going to be a subjective matter unless we accept objective moral values.