It's disturbing how many here are willing to (1) defend Janeway's actions here, and (2) distort what was plainly seen on screen in order to justify their positions.
Firstly, it was not a "scare tactic," she was going to leave him in there until Chakotay intervened, the episode plainly shows this. Interpreting this as "bluffing" is just fan revisionism after the fact to get her off the hook. There's no on-screen basis for believing she was bluffing, but lots of on-screen reason for believing she was NOT, since Chakotay himself plainly DIDN'T.
Secondly, even the episode doesn't portray Janeway in a positive light, as we are not meant to see her that way. She bullies her subordinates, and threatens to kill her opponents, etc. That's why they have her basically apologize to Chakotay at the end. The episode itself is showing she was wrong, but yet there are some who insist that she did nothing wrong and have nothing to apologize for.
Hmmm. I'm not sure that I am defending Janeway as much as wanting to put her actions into the proper context and view what happens on the screen dispassionately. When Chakotay stopped the opening of the rift, Janeway said, "He'll break." Now, to me, that means that she is bluffing, that her goal was not to torture or kill Lessing, but to force him to talk. Again, that is an interpretation, but that is how I saw and interpreted the exchange. I don't think it is "fan revisionism" nor does it ignore what really happened on the screen.
Secondly, what we see of Janeway should not be considered in a positive light. In fact, many of us feel that the episode draws direct parallels between Ransom's actions and Janeway's, hardly a positive comparison. She takes risks with the ship and crew, she puts a person in danger of his life, and she ignores the guidance of her subordinates, very much as Ransom does. The difference is that her ultimate goal was "right" and Ransom's was "wrong." But, as is implied at the close of the episode, the ends don't justify the means. To me, that is the ultimate lesson of the episode.
I do think that her actions were within her authority and taken for the right reasons, whether we like them or not. I also agree that she basically apologizes to Chakotay at the end, at least as much as any superior officer ever apologizes to a subordinate. What I like about Janeway as a captain is that she IS flawed and knows it. She escapes complete censure by following the advice of her crew and by admitting she isn't perfect.