I know this has been brought up before, and I know people are rejecting it out of hand based on personal or moral or legalistic interpretations, but...
I still see the episode as a variation on the ancient possession stories from fables, fantasy, supernatural, and science fiction genres, with a distinctive Star Trek twist this time around. In such stories, the object is always (well usually) to get the original person back. With "Tuvix" it's still that same basic story, but this time they just want us to think about it. It doesn't matter what we believe. Just that we consider the alternatives. There is no right and wrong moment.
This is a very good take on the problem, and one worth thinking about.
And Taya, Tuvok and Nelix are alive too, and they were alive first. Like I said any argument you can make can be just as easily applied the other way.