I dunno, they were both pretty selfish. Janeway doesn't like it when someone takes away her Tuvok
That's not fair. It was hardly a selfish decision. Janeway had to think about the morale of the entire crew, and the fact that they all had to live together for an indefinite length of time. When Tuvix refused to undergo the procedure, he basically condemned two other people, Neelix and Tuvok, to death in order to save himself, and in so doing he alienated the rest of the crew. If Janeway had let him stay, there would've been a lot of resentment toward him, and that would've had a dangerous effect on crew morale and cohesion, something they simply couldn't afford when the crew were stuck with each other and had to work together to survive. It was a harsh decision, but it was the only pragmatic one the commander of a starship in such a situation could've made. And yes, you could argue it was murder, but by that definition, letting Tuvix live would've constituted a double
murder. The whole point of the story was that there was no right answer, that it was an agonizing, impossible choice to have to make.