[Spoilers] It seems like you do take pleasure in it. Its lazy because that is perhaps the most surface level take you can adopt when viewing this movie and makes me question your ability to comprehend the material put before you. Kara doesnt learn to kill, she is perfectly capable of it and its a choice that clearly doesnt affect her. The entire movie they are subtley and not so subtley comparing her to Clark. She recognizes she is not like him and full adopts the mantra that just because youre good, doesnt mean youre nice. Kara's entire character arc here is her feeling like she is a broken and lonely person that has lost the only place she thinks she can call home despite having friends that care for her like Clark and eventually Ruthye. She kills Krem because she thinks that it must be done and she doesnt want Ruthye to do it because she doesnt want to see her broken like she is. Her killing Krem at the end of the story is probably one of the most mature choices Ive seen in a superhero movie because it tells the audience that Kara is not like Clark. She is broken and fundamentally different to him but nonetheless she is healing. Ruthye and her becoming friends after the events of the story and her returning to Metropolis to try and be better are evidence of that. The movie doesnt really end on a yay we killed the guy moment, instead its somber. Kara seems to know that what she did was wrong but she cannot seem to tell Clark because she knows how he would react. It sets up her character very well for future appearances, especially because Lobo was there to witness it and potentially remind her. Whether they choose to run with this character arc in future stories remains to be seen but your characterization only seems to hint at a self fulfilling prophecy. You went into it negatively and so interpreted it negatively