Responding to Dale Sams: Why are you so desperate to convince those who disagree with you?
These are the facts from Star Trek canon:
1. One of Starfleet's missions (indeed, it's primary mission) is to "seek out new life."
2. Sentient lifeforms have what we call today "human rights."
3. Tuvix is a lifeform created by a form of reproduction known as symbiogenesis.
4. Tuvix is a sentient lifeform.
5. Tuvix did not cause the act of reproduction that created him.
It thus follows that Tuvix is entitled to all the rights & privileges of other sentient lifeforms in the Federation. One of those is the right to self-determination.
If the Federation is going to go around blithely deciding what sentient lifeforms deserve rights and what sentient lifeforms don't, then they are no better than Terran governments in our history which systematically enslaved or waged genocide on innocent populations.
I disagree that Tuvok and Neelix are dead. And by your logic, if Tuvok and Neelix went into a chamber of subspace we'll call 'oblivion' and Jack the Ripper came out....Janeway has no right to return Jack to get back her crew.
Tuvok and Neelix have the same rights as Tuvix (assuming that 'Tuvix' isn't a delusional creation much like 'Sam Dale' mentioned above) And your comparison to enslavement and genocide is the textbook example of false equivalency.