Corey despises people that lie constantly. Marcus was one of those guys that lied about the women he was sleeping with and fronting like Grady.
I can't stand that either, so I kind of get it. Marcus always talking about "my bytches don't leave/disrespect me" and trying to use that as a cudgel to beat down on other brehs. Corey just called him out on it, then Marcus copped an attitude about it. Marcus also was taking disrespectful digs at Corey as well that any other coli breh would have taken issue with if they were in Corey's position.
Same thing with Zo, he was being all preachy and moralistic taking up for Grady knowing damn well he (Zo) attacked another Black man on Corey's show over words that cost Corey $20k. The same Zo that also got into it with Freez Luv on the show and that's why Freez stopped coming around.
Anyone else would have gotten rid of Zo a long time ago but Corey, as he said, took a chance on him. Grady was the final straw and Corey told Zo about himself.
And the people taking up for Marcus and Zo are watching Corey and not their (Marcus and Zo) content.