Oh, Atton would be ticked and lose his cool. Just start asking him about Jedi.
Atton: "What makes you think you've got the right to interrogate me on anything? You've got plenty of lives to answer for—all you Jedi do. How did you even live with yourself after Malachor? Is that why you went back to the Jedi Council? Hoping they'd kill you? Wasn't it? Maybe you thought they'd forgive you—sure, you might have thought they'd execute you. But Jedi don't kill, do they? At least not their prisoners. Maybe you were counting on it when you went back in chains. So you got off easy—you were exiled, brushed under the cargo ramp, another dirty little Jedi secret. I'll tell you—all those Jedi at Malachor? They deserved it. Every last one of them."
Exile: How can you say such a thing?
Atton: "Because Jedi lie. And they manipulate. And every act of charity or kindness they do, you can drag it out squirming into the light and see it for what it is. The galaxy doesn't need Jedi arrogance or Jedi hypocrisy anymore."
Besides he's got his own secrets, remember? Glass houses. Not to mention no particular loyalty to anything.
And Carth may not take it very well - who can blame the guy, really? Meets up with the slimebag of a mentor he once trusted with everything, the guy who has been the target of his thoughts for four years. Saul proceeds to prove what a smug jerk he is and torture him. They escape, march up to the bridge (and who else engages solo mode, hands Flyboy a pair of vibroblades, and sends him directly after Saul?), and Saul uses his last breath to f--k with Carth's head. Under the circumstances, his reaction's pretty restrained.
So, Carth needs a planet's worth of time to process it, and make his decision.
"I can't hate you. I tried... I wanted to hold you responsible for all the things you've done. For my... for my wife, for Telos... for Dustil. But I can't...I got the revenge I always wanted when Saul died, but it hasn't brought me the peace that I thought it would...That's why I can't hate you, why I don't want any more revenge. You don't have to be Revan, you can be so much more. Whatever the Jedi did to you, they gave you that chance."