I thought Tuvix was a pretty bad example. The whole episode wrote Janeway into a corner. Unless they were willing to fire Russ and Phillips, there had to be a solution which ended Tuvix's life.
I think they either should have come up with some phenomenon to cause them to become separate again (transporter accident or something), or just not done the episode at all.
they could have wrote it so that Tuvix is eventually persuaded to voluntarily undergo the procedure, sacrificing himself to save Tuvok and Neelix. That would have changed the ending from horrifying to moving.