Unpopular opinion: Cas is innocent
Season 6: Raphael wants to bring on the apocalypse again and Cas is the only one standing between that against the guy who exploded him. He's ready to sacrifice what's most important to him, his relationship with the Winchesters and his siblings, to get the power to save them all. The wall I give, that was extreme, but when he wasn't able to fix it like he planned he took it himself.
Season 7: He is influenced by the leviathans, the biblical evil in him. It was pretty obvious to me: he behaves normal before the leviathans, behaves insane with the leviathans, behaves normal again when realizing something is wrong and fights against it, normal again without the leviathans. And the biggest hint for me: him killing his siblings, he loves all of them and hesitated to kill them in the seasons before that.
Seasn 10 Lucifer: Sam went up and down saying that God was sending him messages about Lucifer as the only way to defeat the Darkness and when it was revealed to have been Lucifer, Cas wasn't there. His self-worth issues were the strongest here and he took on the devil so Sam wouldn't have to.