Season 8 has been an action-packed zombie apocalypse adventure in the episodes that have aired so far as the fighters of Alexandria, Hilltop, and the Kingdom have attacked the Saviors on multiple fronts. Daryl and Rick went on a mission to raid a Savior compound to steal a cache of guns, but it went awry pretty quickly, and it became apparent that Daryl and Rick are no longer on the same page when it comes to battling the bad guys. Rick still sees the value in talking to the Saviors; Daryl is quick to kill. Norman Reedus has this to say about the potential for conflict between Rick and Daryl:
There might be one coming. It looks like there could be something happening. But you know, we're still brothers and we're still on the same team, but the stakes are higher right now.
Daryl and Rick make for one of the most formidable duos of the zombie apocalypse. They're both lethal with a variety of weapons and work well together without even needing to talk things out. If anybody could have gotten the supposed cache of guns out of the Savior outpost, it would have been Daryl and Rick. The guns weren't actually there, but they got out alive thanks to their teamwork. Still, Rick was visibly shocked when Daryl first shot Morales (whose return was ultimately short-lived) and then later took out the Savior named Todd who surrendered. Norman Reedus' comments on the Talking Dead aftershow indicate that Daryl and Rick may find themselves on opposing sides of major arguments, even if they still have their eyes on the same prize of defeating Negan.
While Daryl's brutality is somewhat shocking to see, it's understandable that he seems to have snapped. He underwent some hellish treatment while he was kept prisoner at the Sanctuary, both physically and mentally as he had nothing to do but wallow in misery and stew in his own guilt over what happened to Glenn. The man is clearly traumatized and could probably use some time out of the fight. Given that he's one of the most skilled fighters in the zombie apocalypse and all-out war has broken out, taking a break isn't really an option. Norman Reedus went on to say this about Daryl in Season 8:
He's just got revenge on his mind this year. He's ready to kill everybody, no matter what the group says, no matter what anybody says. He's just like, 'Nah, screw it. Everybody dies.' He's very focused on revenge.
It sounds like Rick might not be much of a stabilizing influence on Daryl moving forward, and Carol has her own troubles to deal with without worrying about Daryl. Dwight probably should watch out for himself if he's ever left alone with Daryl. Even if Daryl is playing nice enough with Dwight while Dwight is their man on the inside, his restraint could very well snap now that he has revenge on his mind in such a major way.