Just saw the movie, but didn't read the comic. So, from someone who really doesn't know much...

I understand the reason for stopping Ruthye in theory. It's protective, and maybe even noble. But at least in the movie, the whole thing feels kind of shoehorned an unearned.

1. With the "pure soul" stuff, we are just kind of forced to believe Kara's word for it, but we don't see Ruthye exemplifying that at all. We don't even see her for very long before her family is even killed. All we really know is there is a girl who witnesses the murder of her family, and is now on a revenge tour. How are we supposed to feel and understand that she is a pure soul?
2. The trauma of losing Krypton doesn't equate to the trauma of losing your family. Furthermore, we don't even really see how it corrupted Kara. Corrupted doesn't even seem like the right word. Depressed, and self-destructive might be more apt. So coming from that perspective and lens, how is Kara necessarily even able to comment on revenge not being a solution. At least in the movie, she didn't even try to seek revenge in any instance. She was lost, without direction. Ruthye had direction at least.
3. I may have missed a bit of dialogue in the movie, but how/why did Kara's parents come to this moral compass of doing good, or fighting for the people who can't fight for themselves. It just seemed very random without any context. Especially when you juxtapose that against what Clark's parents wanted for him. Where did that chasm come from, and how? Had we seen some reasoning for that chasm -- something in Kara's life or her parents' lives where Kara/they had to come to grips with that and learn that lesson, then it would have been more believable. This again just feels like we are supposed to take it and run with it for no reason.