Matt did listen though. It's hard for Emily to reign in her power, and from what he's seen and heard so far has him thinking that maybe she lets her emotions take control. He saw her go overboard on Slate, and he was threatened by her in the van for, what, looking at her? (in Matt's mind at least, he isn't always perfectly self aware) He doesn't especially care if he comes across as an asshole, and he isn't going to lie or let things fester since he knows that that's worse. He tried to change the subject, only Liam answered the duck question and he's sorely disappointed in all of you except Liam lol, and he really didn't take well to the I coulda just killed him argument that Em made. After that he didn't have any reason to hold back since Slate is a decent person in Matt's book.
He already doesn't like people and trust is pretty nonexistent. Emotions aren't his thing, he knows physical tells when he sees them, and he needs to see people actively trying to be decent people in order for him to start to warm up to them. Hence why he was so surprised when Slate didn't just drop him in the fight, and is now trying to look out for the guy just a little bit.
