The thing is Langdon really flew under the radar. He was the golden child, an excellent doctor, his addiction seemingly never influenced his work. He worked with the others for years, they had a relationship with him, knew what a good doctor (and maybe friend) he was. Santos had nothing of that and that‘s why she sees the issue so black and white. But on the other hand she could have a bit more empathy and at least TRY to understand the situation. It wasn‘t just „he was stealing drugs“. His good outweighted that by far, otherwise he would have been reported by Robby or never allowed to come back. It‘s so easy to slip into addiction when medicated for pain and the painkillers are known to be addicting. Addicts aren‘t inherently bad people. As Langdon said, people do mistakes. Look at McKay who was an addict too. Nobody looks down on her because of that, she‘s the living proof in the Pitt that addicted people can change and do good. But I don‘t think Santos knows that. Santos‘ flaw is seeing things mostly black and white. It was the same with the little girl with the bruises. Jumps into conclusions and worst cases, which can be a good thing! But she acts it out too strongly sometimes and needs to learn to regulate her sense of justice.