Just because mother is dying why would one treat her as an inferior incapable of handling the truth ? Infantilizing her by making decisions for her about what will ease her passing rather than respecting her strength and character that give her the ability to deal with the truth ? Telling her a lie might make her passing more difficult as she will most likely see through the subterfuge and feel much worse knowing how little her child thought of her ability to cope with the truth.
I keep finding it so interesting how we humans can have different ways of understanding things.
For the sake of the hypothetical we can assume the mother would believe him/her.
Why would lying to make someone feel better be immoral?
Its all about giving the mother comfort.
he feels pity for his confused mother.
So, this mother is a "confused" person, and God's word says,
"God is not the author of confusion but of peace," in 1 Corinthians 14:33.
So, she is not ready to die right; so it would be wrong just to emotionally euthanize her and send her on not really ready to die with an unconfused and sound mind. So, in case he would be happy to do this, I see a problem with that.
Indeed, there are people claiming to be Christian, but they are not living God's way. And there are unbelievers who claim to pity them. But they do not help them to genuinely get into living and loving in God's peace. So, in case she is someone who is wrong, it is wrong to tell her she is right by making a false confession to her wrong way of Christianity which has brought her to a confused deathbed. Plus, the lier needs to get with God, too.
But, yes, we have humans who are happy to be wrong. There are ones who were extremely feeling happy while speeding along driving drunk, right before they died in a fatal crash and brought other people's children along with them. So, happy is not a measure of morality, I would say.
And being happy to emotionally euthanize a confused person is not right; but, of course, the person needed earlier to get with God so He would make her clear and make her a good example to help people, including her son, before she died.
But it is indicated you do not think she provided him with a genuine example which would be worthy of him to follow; and so he merely pitied her, at her end. That on the overall is not moral, from an emotional and spiritual . . . and eternal . . . perspective, I would say.
So, now you will possibly reword your question, again. It seems you are steering your rewording in a direction to hypothesizing that there is no God and so her son is right to be happy and she has to be confused by being any sort of a Christian. Well, if there is no God > that would leave the evolutionary "survival of the fittest" possibility, I understand.
She would be only a bunch of molecules and atoms and photosynthesized sun energy going into recycle mode. Making her feel good for an instant . . . I guess . . . would make no real difference. The neurons would fire up, some oxycontin would flow, then the light is out. And the molecules and atoms and converted sun energy can be recycled in other life forms and as nonliving materials.
But, of course, he might feel good. And if this is your standard for what is moral, then by your standard it would be moral.
But if there is God, she could die and then find out he lied to her. Also, if she really was confused because she was not with God and ready to die well . . . already for years she has been fooling herself; so her son keeping that going instead of trying to help her would be him only helping her to keep fooling herself so she would die confused.
I mean, in case you can understand my explanation > if he makes her feel good - -
by confessing to her false way of Christianity which has gotten her into confusion instead of with Jesus in "rest for your souls" (Matthew 5:46) . . . then he would not be loving her, in my opinion. But even if he prayed for her and used scripture to try to help her, she could have become hardened so she would not listen to him, even at her time of death.
Maybe you will reword your question now, with other than an eternal or evolutionary perspective to it? Your hypothesizing seems to be steering and re-steering so only your answer can become acceptable. Be we are in a Christian forum, where we do share Christian and Biblical perspective.