I neither like nor hate Janeway but my position on her decision regarding Tuvix has changed over the years.
Did she murder Tuvix? Of course she did. There is no other way to interpret her decision and there is no way she would have been allowed to make the same decision if she had been in or near Federation space. If she had, she would have been spending a real long time in a penal colony.
But out on the frontier and out of contact with Starfleet, she has a duty to the other 140-plus people under her command to do her job to the best of her ability. In order to do that, she needs the people she trusts and that is Tuvok and to a lesser degree Neelix.
If she loses a crewman or two to rescue someone important to the operation of Voyager
, does that also constitute murder? When Spock and good-Kirk conspired to force evil Kirk onto the transporter pad against his will to cure good-Kirk's sudden inability to lead, does that constitute murder? When Troi orders holo-Geordi into the fire at the expense of his life in order to save others, does that also constitute murder in real world conditions?