I think a huge problem with why this topic is going in circles is that people aren't arguing the main point.
Stop arguing whether Janeway did the right thing or not. There will always be a difference in opinion.
What should be talked about is whether Janway's actions meets the definition of murder. No matter how much you disliked Tuvix or wanted Tuvok and Neelix back, it was murder. Janeway took Tuvix's life away without his consent.
You can think Janeway did the right thing (I don't), but she still murdered Tuvik to get her two crewmen back.