I do have to give it to Voyager in this circumstance, this is one of the few times they don't take the easy way out in a plot, and Tuvix conveniently sacrificing himself would have been very expedient for the plot. I just wish they would have thought about what they were doing in the end, because they really made their heroine look bad.
I also understand the intent. Janeway's in charge and they want her to be the one making the call. But like in Caretaker, the writers focus so much on Janeway making -the- call, they don't stop and think about what call she's making. In Caretaker, Janeway orders the Array destroyed to deprive the Kazon of it instead of using it to get home. But when you stop and think about it, they already drove off the Kazon and they could have used it to get home and used an explosive device with a timer as it's detonator. So in exercising her authority in that one she just seems stupid.
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.