How about historical precedent? Gods did arrive on Spanish ships to South America.
>So children are good, and just because not everyone agrees on that doesn't somehow make children not good.
I can't make sense of this statement. If my terminal value is that children are bad then that's it. How can you even start argue with that?
They are slaves. But it does not really matter. I may be wrong. You may be wrong. We may have different terminal values. Point is, not all people think that children are good even right now, much less in far in the future. Idea that grabby civilization will consist of many individuals is not given. Who knows, may be they even become singe individual. Sound like a bad idea to me now, but may be it will become obvious choice for future me?
I find an idea of having children to be morally abhorrent. Granted, right now alternatives are even worse so it is lesser evil - but evil none the less. Presumably grabby civilization able come up with better alternatives. Maybe you will become individual of grabby civilization, individual with great personality and rich inner world spanning multiple solar systems?
In this scenario we giving the doctor an awful lot of power. We need to have unreasonably high trust in him to make such choice practical. Handling other people lives often have funny effects on one morality.
There is another problem: In reality, shit happens. But our intuition says something like "Shit happens to other people. I have control over my life, as long as I do everything right no shit will ever happen to me". See? In my mind there is no way I ever need organ transplant so such arrangement is strictly detrimental, while in reality chances are I will be saved by it. Again there are good reasons for such intuition, as it promotes responsibility for own actions. If we are to make health "common property" who will be responsible for it?
I suspect it is easier to solve artificial organs than human nature.