There's no "right" decision to be made here. That said, I don't approve of her decision, I do consider it murder, and I wouldn't have made the same decision she did. Either way though, the decision-maker will have to carry quite a burden. Regrettably we never saw any acknowledgement of that. Thank God they included the Doctor refusing to perform the procedure.
I would have given the Voyager folks massive kudos if they'd had the restoration attempt fail though, and Janeway had lost all three of them. I'd have also liked any sort of follow-up to this on the part of Neelix and Tuvok and how they felt about Janeway's actions.
I've asked this before and nobody's ever given an answer that I'm aware of: if Tuvix is allowed to be killed because he's not considered a being with the right to life yet, how long must he be allowed to exist before he is granted that right? Weeks? Months? Years? Never? When does he get to stop living his life knowing it might be taken away from him at any moment?
Question - was there some sort of rush to restore Tuvok/Neelix? If not, it seems prudent to ask why nobody apparently pursued the option of recreating Tuvok/Neelix -without- destroying Tuvix, especially if there wasn't a ticking clock.