I would say Neelix is a big part. Starfleet officers have already consented to the possibility that they might be ordered to their death for the good of their ship or the Federation. While their transformed versions may not have been exactly the same beings as the originals, there is still some ethical cover in that some version of them in the past had accepted these risks. Neelix, however, was not a Starfleet officer and had made it very clear that he did not consent to having his life sacrificed for the greater good of Voyager.
Just how much this ethical baggage from either side carried over to a new being is unclear; it certainly would have been less unclear if it had been two officers merged together and not a civilian passenger.