What if Carlo meant to get himself killed at the auto-da-fe...
His diplomacy isn't working, he doesn't really have confidence in his ability to lead a revolt, he's lost Elisabeth, his father doesn't love him, Eboli could make his life even more hellish at any time (and he blames himself for her discovery and endangering Elisabeth)...
He decides to give the rebellion a high-profile martyr, and proclaim his support for their cause in a way that can't be ignored.
Force Philip to strike him down in public and take on the label of filicide, however justified he might think himself, in a way that can't be tidied aside by court proceedings or political lies around a planned execution.
Inspire the people to avenge him, show the rebels that their cry was heard and the prince himself gave his life for them...
But of course Rodrigo can't let that happen, and in the moment of truth he chooses his Carlo over the cause, even as his act seems on the surface to be betrayal...
