What if Tuvok and Neelix were "screaming inside" to get out? They weren't, unless you think Tuvix just lied. Being he was honest enough to brand himself a coward, I doubt he'd have failed to mention it at the beginning. He clearly stated there was no multiple personality disorder and that he just had both of their memories.
Sure there are places where the captain might have to order a crewman to sacrifice himself for the good of the ship. This isn't one of them. To say this was one of them is blatantly an insult to anyone who might sacrifice themselves. If Tuvix -volunteered- for this you could call that a sacrifice as it would be his to make.
As for this decision making Janeway "interesting" and more human? What the heck? She's the main protagonist of the series and a Starfleet captain. Could you actually picture Picard or Kirk murdering a member of their crew against their will? Gul Dukat was an interesting character, but a good guy that does not make him.
You can justify her actions all you want, that's all it is, a justification for murder and a very hallow one. Janeway is the captain, she's not god. Frankly it was arrogance of the first order for her to even presume this was her choice to make. To say nothing of lacking morality, though this is hardly the only morally lacking choice she makes.