He didn't give his father any benefit of the doubt, didn't listen to his story, and didn't believe Walt's denial of killing Hank..Walt said that he didn't kill Hank, why didn't Flynn believe him?..why didn't he take a moment to think about while he was in the car with his mom and after he began speaking to Walt?..
I knew at least 5 kids growing up that discovered their parent/s were drug dealers, and barely gave any , tbh

..your parents are providing for you by any means possible, that's how most people in real life react to this type of discovery, tbh..Flynn hasn't been in any danger(so far) by Walt's actions, yet he completely turned on him for something that he hasn't even confirmed yet?.. he severely overreacted, tbh..
I understand being distraught over the revelation of Hank's death, but why didn't he give Walt the benefit of the doubt?..Skylar asked Walt if he did it, he said no, why didn't he believe him?.. ty son, tbh..
He also saw his mom pull the knife on his dad, why isn't he angry at his mother?..if I saw my mother pull a knife on my father, I wouldn't blame it on my father, tbh

..especially since Flynn already discovered that Skylar knew about Walt's profession, this wasn't fresh to her..
And again, as for Hank, he's a ing DEA agent, he was always at risk for trouble, tbh..it's the life he chose to involve himself in..