Now, we might consider someone selfish for not doing so, but I hope no one would ever argue that someone should be *forced* to risk his or her life to save another.
As a comparison, let's look at the choice Captain Picard had in The Enemy
. The gravely injured Romulan needed to receive what was essentially a blood transfusion from Worf to survive. Although Worf refused he did state that he would comply if ordered so to do by Captain Picard. The stakes in this situation were not only the life of the Romulan, but also the possible outbreak of a war between the UFP and the RSE. The costs in this situation were ordering Worf to undergo a medical procedure (likely minimally invasive and not painful) by denying him his freedom of choice and potentially causing him psychological damage. Picard risked the life of the Romulan, the lives of the Enterprise crew, and a potential war with the RSE all to preserve the rights of an individual.
If we look at the characters of Tuvok and Neelix (and generically most characters in Starfleet) they had demonstrated their ability to perform acts of self-sacrifice to benefit their friends and crewmates. It is an odd (inconsistent) choice, I believe, to have written Tuvix (who was the sum of Tuvok and Neelix) as a character who was unwilling
to make the supreme sacrifice in order to restore his progenitors.
Since UFP society has evolved to the point where being a good person was life's ultimate goal (rather than fame or acquisition of material goods), acting selfish would probably be viewed as one of the more abhorrent of social transgressions. Perhaps it was Tuvix's violation of the fundamental purpose for human existence (self-sacrifice) that Janeway decided he no longer deserved to his rights, including the right to live.
What do you think of the following change to the plot? What if the Tuvix character had been written so that this apparent contradiction between his personality to that of Tuvok and Neelix had not existed? What if, instead, the plot's conflict was not that Tuvix wanted to live and everyone else wanted him dead, but was instead Tuvix was a character who desperately wanted to give up his life to restore Tuvok and Neelix, but the rest of the crew argued and did what they could to prevent his "suicide", because
they believed so strongly in his right to exist, despite the circumstances of his creation?
Then the moral dilemma would have been everybody wanting to do the right thing but having the consequence meaning that someone (the group or the individual) had to suffer, rather than everybody having to do the wrong thing (Janeway by killing Tuvix or Tuvix choosing to live). At least this scenario would have allowed the characters to act in a way which was consistent, rather than having to shoehorn in a dilemma.