They was a voyager episode too.

There is no morality or immorality in it, she is responsible for her crew, tuvix wasn't crew but the other two were.

You didn't murder anything, we have several examples of transporter patterns living out their lives in holodeck simulations.

Tuvix wasn't some alien body snatcher who possessed the bodies of the deceased. He was literally Tuvok and Neelix living on in a new form, which comprised a third entity.

In killing Tuvix, Janeway also murdered both Neelix and Tuvok.

What she did, in essence, was to murder three people to bring back two.

If someone's heart stopped in a hospital, then an alien possessed their dead body and said "I was just born, this is my body now, your guy was dead" I don't think anyone would argue that the person's heart could very much be restarted (assuming otherwise healthy) and the alien has no right to use someone else's bits.

A better analogy would probably be, if an alien used the body of a cryogenically frozen person that we KNEW could be revived with 100% certainty.