IMO, once Neelix and Tuvok stop existing, they are dead. They have no consciousness, they aren’t around. They’re gone. They’re ex-people. They’re not sad about the situation, because they no longer exist. There’s no brain there to process any of this. Once you are dead, you don’t have a right to live, especially not if it means the death of another.
Tuvix, on the other hand, existed. He was conscious, self aware, intelligent, alive. He was dragged, crying, begging for his life, pleading for anybody to step in and stop him from being murdered. Then he was killed to bring two people back to life.
Now I know people will say “but 2 is more than 1, so it’s fine to kill him”, but that’s never sat right with me. What was that Picard speech about arithmetic not being a good reason for discarding the rights of sentient beings?
Tbh I’m astounded the Star Trek community is massively on the “murder of an innocent is ok if it saves more people and he’s a little ugly” side