And I suppose that to you, Janeway broke no rules when she was willing to let Lessing die?
As everyone knows, Chakotay's interference prevented us from knowing what Janeway would have done a few seconds later. But this simple fact is commonly ignored. But let us hypothesize that Janeway, whether intentionally or by misjudgment, had actually let Lessing die.
I reject your argument from depravity that equates Lessing's imaginary death with an injustice. Lessing murdered people, of an unusual and technologically primitive sort, it is true. But he was still a murderer. It takes barefaced gall to whine about Janeway breaking rules in the purely hypothetical case of Lessing's death, while blandly pretending that she didn't also break rules in allowing Lessing his freedom.
Lessing got away with murder because Janeway was a tyrant? She was too soft on him. Letting him off just because he was following Ransom's orders was highly objectionable. He was even worse than the Maquis.
As for the assumption that Lessing was tortured, Janeway didn't personally threaten or harm him. She merely left him outside Voyager's protection so that he would face the fellows of his victims. The notion that humans are so privileged that ugly primitives have no right to exercise justice on them, even upon murderers, is absurd. And it may be a science fiction story, but that way of thinking still smacks of something really ugly.
Thinking about the ethical implications of Tuvix is a waste of time. Insofar as it is a metaphor for abortion, the episode falsifies the issue by assuming the fetus is indeed a person. Insofar as it is a metaphor for capital punishment, the episode falsifies the issue by making the death of one literally restore the lives of two others. Insofar as it's not a metaphor at all, the science is too bloody stupid to take seriously at all, no matter how sensational it all is.