Indeed. I have no idea what all of this has to do with organ donation by the way.
It was horrible accident as death and birth went hand in hand and as the process is reversible.
This makes it psychologically much more difficult than just death (which is of course already hard enough). It's kinda like when a mother dies during birth. If the father wasn't too eager to get a child in the first place he might blame this child for the death of his wife. It is understandable and human but it is also detestable and irrational.
So let's think about Tuvix in a rational way. Either he lives on while Tuvok and Neelix remain dead or he is killed such than Tuvok and Neelix are resurrected. Whatever you do is wrong. And no, Tuvix acting as a constant reminder that Tuvox and Neelix are no more because he is a merger of both (or in short, that he is a freak) is no argument for his death. In matters of life and death we should really try to be as rational as possible.