If killing Tuvix to save Neelix and Tom is morally okay, then it's also okay to kill a poor person on the street in order to harvest their organs for rich people who need them.
One person died and two or three more 'contributing' people got the hearts and livers and kidneys they needed to live, must be ok cause the numbers are on your side, right?
And Guy, putting aside your religious refusal to accept the internal logic of the show regarding artificial intelligence. The lightbulb's programming was not capable of taking any action that would directly result in a loss of life. The Hippocratic Oath was hard coded into him, and he can't kill any more than Internet Explorer can render large DOMs.