R. Star wrote:
You can argue that Tuvix is morally a coward for not willingly sacrificing himself.
Yes, you can. And if Tuvix truly remembers what a Starfleet officer is expected to do - lay down his or her life to save a crewmate - then it is indeed cowardly for him to insist on putting his own life above that of Tuvok and Neelix.
Besides, Tuvix should have remembered the Vulcan logic he got from Tuvok. To restore Tuvok and Neelix is the logical move. There's no advantage to Tuvix's existence - he's not a better tactical officer than Tuvok, nor is he a better cook and ambassador than Neelix. And the principle of the greatest good for the greatest number is also a logical one as well.