Castiel didn't disagree that Raphael had had it coming. He and Raphael had been engaged in battle for some time, each side playing dirtier and fighting harder. Raphael had had numbers and power on his side, angels who weren't willing to disobey the order of an archangel.
"It started with me," Castiel admitted. "And then a handful of others. And then more of us... we never outnumbered Raphael's supporters. We had to do things, to overwhelm them. It ..."
Relatively insignificant angels like Castiel didn't have free will. They didn't have the ability to make choices on their own or command their own destiny. They simply weren't created that way. While defying an archangel, while leading a ragtag group of Heaven's rebels, he was also testing out his ability to make big decisions on his own for the very first time.
Of course he'd screw up spectacularly.
"I was the one who did it," he said quietly. "If you're curious."
It shouldn't have been possible. Castiel was nothing compared to Raphael. Even at full power with all the intensity of his grace, he could still be snuffed out like a candle at Raphael's will.