Dale Sams wrote:
But in the end, it's really no more 'murder' than hypothetically ordering Geordi to expose himself to lethal radiation to save the ship.
Exactly. Since Tuvix was still a Starfleet officer - Janeway recognized him as one, at any rate - it would be his responsibility to sacrifice himself for the greater good. That's what Starfleet officers are expected to do. It's expected in any decent military force, real or fictional.
With Tuvix it's no different. If he wishes to consider himself part of the crew, he is required to follow all orders given him
. Up to, and including, laying down his own life.