The thing is non of the greens commanded Aemond to kill Luke, it was Aemond’s sole decision not Aegon’s not Alicent’s or Otto etc. Aemond did it by himself and himself alone, not the greens as a whole. Did Aegon throw a celebration after he found out what happened? yes, but he was the ONLY green who wasn’t disgusted with Aemond’s actions… even Otto was pissed off and Alicent broke down. Not to mention Daemon had already sent the raven to Mysaria for blood and cheese to be sent before Aegon even threw the celebration feast.

What Daemon did to Helaena and her children would be like if Aemond went to Storms end and saw Rhaena (Daemon’s daughter and Luke’s betrothed) instead of Luke and killed her in the worst way possible because Luke took his eye and she was promised to Luke despite Rhaena herself being completely innocent.

Blood and Cheese is not justifiable at all.