Yeah, Kakashi did seem kinda sad when thinking about Obito.
Maybe that's the reason, his best friend tried to kill him, so he feels betrayed and sad.
But has any of you given a thought that maybe Itachi is lying, I'm talking about how you get the Mangekyou Sharingan. I know what Itachi said but his dad never actually told Sasuke what it was anything other that it was a terrible condition to be met.
And the only thing that we know is written in the Uchiha shrine is, according to what Itachi said, the purpose the Doujutsu originally served, not how you get it.