In my experience, there are people who will consider ANYTHING to be immoral, especially if it was invented in the last 100 years. I'd say 'regardless of whether or not it can save lives', but some people seem to get EXTRA offended when science offers to save lives.
Not to sound too intolerant of religious folk (though with this specific sort of religious folk, I'm not all ashamed to admit that my tolerance of them is... lacking...), but if your moral code considers it immoral to save lives, you need to re-evaluate your moral code. I mean, if there was some legitimate downside, I'd be more open to their opinions, but there isn't. Dead people don't need their organs anymore.
I, personally, am proud to have checked the box consenting to organ donation. When I die, at least I can go with the knowledge that my death might have a bright side to it. Maybe my passing can give someone else a new chance at life.
... granted, my liver and kidney probably aren't in the most salvageable condition... but I'm sure I've got something else that's a little more pristine.
In comment to the original question, I would ask this:
Is there anything in this world, anything at all, that someone does not find immoral? Is there a single act of kindness that someone can not find fault in? Are there any evils that were, at one time, socially acceptable and considered good and honorable in some other distant time or culture?
This leads to much bigger questions, though only one which I find important. Is morality not but an illusion; a security blanket we cover ourselves in, so that we can feel safe and warm? This blanket we cling too makes us feel good, but it also separates us, defines us as good and others who disagree as bad. Morality itself is good, on the surface, but if it drives us apart is morality itself not also an evil?
I like to keep a pretty down to earth view of morality. If you're hurting people, its bad. If you're helping people, its good. If you're doing neither, its ethically neutral. If it gets any more complicated than that... eh, I deal with it on a case-by-case basis.
I don't believe there's any sort of divine morality imbued into all of us (i'd have to believe in the divine to believe that), but I don't believe that means that morality is necessarily a free-for-all. I believe there's fairly objective criteria that you can use to sort out the good from the bad.
Perhaps I'd think differently were I born into a different culture, or simply given a different upbringing; but, at least from where I'm standing, my view on morality seems fairly rational.
To widen the list of religions that oppose it, add Christian Science and Shinto. ( Not sure if Gypsies count )
More about this here:
Huh, Shinto? Wasn't expecting that, but I suppose I should have, considering their beliefs concerning the impurity of dead bodies.
Sidenote: Isn't 'gypsy' considered a slur? Not calling out TaintedAndDelish or anything, I see it ALL OVER THE PLACE; but it was my understanding that Romani generally consider the word offensive, or at least, not what they prefer. To be fair, though, I don't think I've ever actually met anyone of Romani heritage, so... yeah, I'm going purely off of what I've heard and read.
I wonder if there's another reason. My own mother was against transplants, not for the moral issue, but a health issue. She supposedly cited (this is from years ago so my memory of it is incomplete) that transplants actually make a situation worse, not better, and that was why she was against it. Me... I plan on getting cremated so might as well use the damned things if they're still healthy enough to help someone else. I've actually considered doing a living donation (such as kidney) but I have chronic anemia and that may cause issues in itself. I can't even donate blood. :/
Well, at least in SOME cases, the alternative can be fairly grim. I fail to see how a transplant could conceivably make the situation worse than 'certain death'.
On the off-topic subject of funeral methods; I feel like all the ways I'd like my body to be handled are a touch... extravagant.
One would be this: https://urnabios.com/
The other would be a good ol' fashion Viking funeral.
Depending on how civilian space travel is at the time of my death, I could totally dig the whole 'Spock' type deal.