Chances are if Janeway had gone the other way and kept Tuvix alive at the expense of Tuvok and Neelix there would be just as many people, if not more complaining about how unethical she was.
Exactly. She was in a no-win scenario.
And, as I said earlier, the choice seems (a little) less risky for the "Tuvix must live!" supporters because neither side had "regular" (human) loved ones. Tuvok's family were 70 years away from discovering what happened, and would perhaps accept Janeway's logic in saving Tuvix. Neelix had no family left whatsoever. (I can't recall whether Kes, another alien, was leaning towards saving her lover, Neelix, and mentor, Tuvok, or the new entity, Tuvix.)
Had the episode been about saving "Tomnaomi", a creature created by an accidental joining of Tom Paris and Naomi Wildman, Janeway and the viewers - and Samantha Wildman (who would be travelling with her loved one's child-killer for up to 70 years) - would have had an even more agonizing decision.
The decision in the episode was supposed to be agonizing because its an ethics question with no correct answer.
Every day, human women of the 21st century make the agonizing decision to abort their unborn child, a person with untapped potential, to save their own lives, and the "right to life" movement say that they're wrong to do so. The question is only made (relatively) easier because the child hasn't actually arrived yet to speak for itself, which Tuvix was able to do, and medical science is a littler cleverer than it was in the 20th century.