In Tuvix, Janeway again makes the call. Clearly they thought it out as Tuvix uses this argument in defending his own life, that it's not Janeway's call to make. But Janeway's the captain, she's making the tough choice, even though it's not hers to make and she's playing god with people's lives and taking one against his will. It's definitely a moral dilemma, but it's not Janeway's to resolve.
Picard certainly would have given a stirring lecture about how the greater good should compel Tuvix to make the proper choice. Kirk probably would have insulted him into doing it by shaming him with his cowardice. Sure, Janeway isn't Kirk or Picard but I don't think either of them would take a man's life against their will in this circumstance. As for it making Janeway "more human" somehow? I don't see it. She's not the "hero" in this episode and is acting downright villainous.
It's not the last time Janeway will play god with people's lives & make tough calls that aren't really hers to make. I think that in trying to make their woman captain appear strong & decisive, they turned her into someone who makes a decision, then wallows in guilt over it later. Can't really go into any more detail at this point in the series.
I'm not sure the "greater good" means that Tuvix has to sacrifice himself. Chakotay (wuss who says nothing when Tuvix is pleading for his life) said that Tuvix was an example of the whole being greater than the sum of his parts, and Janeway's log praised him as more than competent as both a chief of security and a chef.
As for making her more human, it's the flaws that make us human. And heroes don't always act heroically. Sometimes they're driven by the same emotions the rest of us are.
