Jamie made a difficult decision to protect his family. This isn't the first time he's had to do this. Outlander Season 5 hasn't made him a murderer.
Fans are divided over Jamie's actions on Outlander Season 5, Episode 5. That's not all that surprising, but his actions didn't "make him a murderer." The show hasn't changed Jamie's character suddenly. This certainly isn't the first time Jamie has taken a life to protect his family.
One of the complaints of book fans is that this storyline has been fabricated for the sake of the Regulator storyline. From a show point of view, the storyline was excellent. The series tells the story from a third point of view, showing the Regulators' actions and not just telling the story.
However, before jumping on the writers for "making Jamie a murderer," it's worth noting that he made a difficult decision to protect his family. Killing Knox wasn't something he did because he wanted to. He did it because he needed to. Had he not killed Knox, There's no doubt that Knox would have turned Jamie over to the authorities.
This isn't the first time Jamie has taken a life to protect himself, his family, or other people he cares about. In the first season, he took the life of a Redcoat deserter to prevent Claire being raped. In Season 2, he killed Dougal in self-defense. He certainly didn't look at Murtagh in a different way when Murtagh killed Lord Sandringham to protect Claire and Mary. Remember a lot of these storylines have come from the books and not just show invention.
We have to remember that Jamie is a Highland warrior. He's been raised to protect the people who have needed it, raised to do what needs to be done. This is just another one of those situations.
Jamie doesn't enjoy taking lives. At no point did he want to kill Knox, but he knew that he had to. He's not going to feel sorry for protecting the people he loves. Don't ever expect that to change.
Outlander Season 5 airs Sundays on STARZ.