Janeway Murdered Tuvix once.
Tuvok and Neelix murdered the man 9 times a day for the rest of their lives every time they thought about putting the band back together until they reached the final conclusion "Nah-fuckit."
Neelix is practical, he's going to get that nice girl he met to sign a prenuptial agreement attesting that she is not going to stop frakking him if he gets converted into some sort of thing by a transporter accident.
What happened to Neelix, already already to his sister. The entire population of a moon got turned into a single cloud like entity monster which gave Neelix nightmares and caused him to desert form the space army rather than avenge his sister smited by the meteron cascade.
BY that reckoning Neelix spent the last twenty years already committed to the foregone conclusion that Tuvix was the absolute worst thing that could happen to him.
Non resus order in case it all got horribly worse vs. heroic means to reverse the procedure.