This shouldn't be a dilemma, but it is.
I wrote a book about my family history, and as I had a couple left over after giving them to my family (siblings and their children), I sent one of the extras to a cousin (I haven't seen in more than a decade).
It was an interesting book, filled with stories about ancestors who were pirates, canonized saints, an ancestor grandfather who was kicked out of Plymouth Colony for being Anabaptist, and then later jailed, fined, and whipped for allowing a Quaker in the house. I told the story of one priest who was hanged for trying to get a woman burned at the stake for witchcraft because she wouldn't sleep with him. (Quite a colorful family history and this is only a tiny part of it that is all documented in reliable sources.)
She sent me a "Thank You" note with a comment that I through the stories, she sees that I seem to have a rebellious spirit. She didn't say it in a rude way, but she concluded the letter with why she is a Christian and how much comfort it gives her and how her son-in-law graduated from MIT, so he's a scientist, and most scientists believe in God.
How she concluded that I don't believe in God, I haven't a clue. It's not that I try to hide it. I simply don't make an issue of it.
I am torn between throwing her letter away or responding to it. Part of me want to write a kind and respectful letter telling her why I don't believe in Christianity, and why I believe that Christianity has so distorted Jesus' teachings (through its reliance on Paul) that it has gone far astray from the initial message. I believe that Jesus was a spiritual atheist and I want to quote his words as evidence.
I want for her what she wants for me. I want her to see a kinder and gentler way to live her life and I want her to see the difference between what Jesus taught and what Christianity teaches. And I want to end it by saying that I'm an atheist, as I think Jesus was, and how much better my life is as a result of it.
But I know that I have never had a conversation with a Christian where I was not defending Jesus, with the Christian calling me a heretic (and worse) for simply quoting the man. Perhaps I should just quote the science that my worldview is based on?
the letter is 5 pages long approaching the subject from a christian rather than a scientific perspective. It's still in my computer.
Should I send it? Should I rewrite it from a scientific perspective. If I send the letter, am I lowering myself to Christian standards? I certainly don't want to do that! At the same time, Christianity has become so dangerous in its treatment of women, LGBT, and non-Xians, that I feel a responsibility to point out how Xians are being cruel tyrants. After all, the 1939 German census shows that 93% of the population was christian, and look what they were willing to do. In some ways, responding to her is an ethical imperative.
Two days of musings haven't pointed me to a comfortable solution.
Personally I would respond to the letter. I would do it with facts, including the fact that most scientists are NOT religious. I would be kind, and not make her feel dumb, but show that you don't agree, and that Atheists are good people. xtians don't get to claim the only good values.
Me? I wouldn't respond. You haven't seen this person in more than a decade. What's the point? She believes in her invisible magic ju-ju spirits, and I doubt anything that you say in a letter will have any effect whatsoever on her faith in the non-existent. Let's face it. The "true believers" are insufferably arrogant about their faith, while putting on an act of being ever so humble. If you really want to re-kindle the relationship with her, I'd go with Karim's suggestion and ask to lunch. But, skip the topic of religion.
I think I would not respond. Then again, I am not into confronting people. Live and let live. Also, my family has pretty much died off, and the few remaining have nothing to do with me, so what do I know.
At some point, I feel you challenged her belief system with your historical depictions of Christianity's excesses. Let it steep in her mind, and as for her responding, it was probably more to reassure herself than to convince you. And if I know my good Christians, it was a take a hike, I am satisfied with my delusion letter. The MIT-Grad-believes is her way of dismissing science. Stay safe, and stay clear. Not everyone loves truth. You could post the letter here or on its own thread, as most of us would enjoy it.