[ Kakashi doesn't has an answer for either question. Not a good one, anyway.

He'd largely not gone out of his way to speak to Mikoto because speaking to her only reminded him more of how much he failed Sasuke. His inability to be a good sensei to Sasuke directly resulted in the boy not only leaving Konoha, but also killing his older brother to avenge his family.

As for Itachi --

Whether or not it was his fault, he still carried out the killing when he didn't have to. And though Kakashi is sympathetic and understands why Itachi did what he did, it was still wrong. ]

He made the choice to follow that order, Kushina-san. That was his decision.