Sorry, this is long and rambling, but there were several points brought up that I wanted to discuss.
First of all, Mother Theresa was a nun. She had taken a vow of obedience. It is most likely that she did not forbid the publishing of her works. There is a long tradition of saints asking to be kept from the limelight (out of humility and a sense of unworthiness), and a long tradition of superiors insisting that the saints be shoved back into the limelight so that the world can profit from their influence. It’s intrusive and disrespectful by modern standards, but monastic life in general often seems intrusive and disrespectful by modern standards.
Also, although the letters were between her and her confessor, they were not confession. Confession cannot take place by letter.
So basically, while the publishing of this book may seem unethical to us, it is consistent with the social contract that Mother Theresa willingly entered. If she felt trapped by that social contract later on, then that's a shame, and if she (wittingly or unwittingly) caused harm because of her misery, then that's tragic.
Mother Theresa’s doubts and trials will not necessarily be frowned upon, nor are they unknown within the church. My youth group leader, a brilliant and intellectual Catholic, told me in about 1999 (two years after Mother Theresa died) that Mother Theresa had suffered from “spiritual dryness” (i.e., loss of joy and zeal) for most of her life. The Catholic church does not teach prosperity theology. It teaches that God wants the best possible result for the world in the end, but he’s not afraid to crack a few eggs.
Some reasons given for spiritual dryness among saints are:
1. Spiritual dryness is suffering. Suffering is good because:
a. You can offer it up to God to reduce evil—in your soul, in the world, in the sufferings of the souls in purgatory, etc. Suffering embraced means less total suffering.
b. It’s good for self-discipline.
2. Spiritual favors (e.g., joy in prayer) are a gift from God, and he gives them out as needed. Perhaps this person was strong enough not to need them.
3. The more good you are doing for God and the world, the more the devil wants to trip you up.
Canonizing a saint does not clearly fall under papal infallibility, although I’m not sure where it does fall on the spectrum of “Catholics must believe” to “Catholics may believe if they like.”
I wonder how many saints were really just suffering from mental illnesses. My mother once had a manic episode that, in another time and place, would almost certainly have looked like a visit from God.
http://www.albany.edu/scj/jcjpc/vol8is1/reda.html
This essay makes what appears to be a compelling case that St. Catherine of Sienna suffered from anorexia nervosa.
And all that humility and self-abnegation that saints employ? Oh God, I am not worthy, and all that? It sure looks like depression to me.