There's a lot of comparison to the 7 of 9 situation. In my opinion the same principle applies both times, and that's why the decision is correct both times:
7 of 9 was born
Annika Hanssen, a normal, intact human being. She was assimilated against her will and her entire being subsumed and twisted. Seperating her from the Borg collective is merely restoring her to her natural state
. What happened to her should never have happened in the first place. Exactly the same goes for Tuvok and Neelix - seperating them out again restores them
to their previous natural state, nothing else. In fact it could be argued that letting the "merged" creature continue to exist, that would in effect have ended the life of two
distinct individuals. I still don't see how that could even have been considered.