Yes, Janeway ultimately decided to proceed with the separation and performed the procedure herself (succeeding in restoring both Tuvok and Neelix), after the Doctor refuses to take Tuvix's life in compliance with the medical precept of doing no harm* BUT, I remember 2 things too.
1) Kes reaction: she reacted poorly to Tuvix as his existence deprives her of both Tuvok and Neelix and though her displeasure lessens over the course of the episode, she never completely goes away. She will end to ask Janeway to do her utmost so that "her" Neelix (and Tuvok) returns to her -> how couldn't she not know that for restoring of lost Neelix and Tuvok, would require Tuvix's execution?!
2) while Tuvix made a final emotive plea for support from the crew on the bridge, NO ONE supported him. Whether it's Chakotay, Tom, Harry or B'Elena, again, NO ONE even tried to intervene with Janeway (they kept silent and lowered the head), not even when she asked to the security officers to escort Tuvix to Sickbay, even though he just recognized that "the needs of the many outweigh the needs of a few" and consented to his fate -> He wouldn't have tried to escape or tried to take Janeway in hostage during the transfer. Come on, can you imagine Tuvok or Neelix doing harm to their beloved Capitain or not obeying to one of her orders?!
For me, they ALL share the responsibility here, not only Janeway (besides, at the very end, we see a troubled Janeway after performing the procedure and how she is going to have to live with her choice). I am almost sure that for the others, it was just an accident, nothing more.
I like this episode for Mulgrew's (she really brought that look and emotion to work with her) and Tom Wright (Tuvix)'s great performances. He marveled at his ability to bring credibility to the prospect of two characters, Neelix and Tuvok in one.
