The title of the play All My Sons is justified because Joe Keller should have thought of all the pilots who flew in planes that contained defective parts his company sold the government as his sons metaphorically. He should have put their safety and the safeguarding of their lives above the loss he would have taken had he acknowledged that the airplane parts were defective. Instead, he pretended that they were fine and sold them, knowing full well that they might (and in many cases did) fail.
Because of Joe’s callous disregard for the lives of others and because he placed his profit above the safety of the young men in those planes, he was indirectly responsible for the deaths of many pilots during the war. Moreover, he was also indirectly responsible for the death of his own son Larry.
Joe acknowledges this at the end of the play when he is confronted by his family and Annie. He is facing the prospect of going to jail for his actions during the war. He realizes that Larry understood that he breached his communal and moral responsibility by putting his economic interests above the lives of others. Based on the letter Larry sent Annie, Larry essentially committed suicide.
This means that indirectly, Joe is just as responsible for Larry’s death as he is for the deaths of those other young men who relied on his plane parts to work properly when they were flying on wartime missions. Speaking of Larry at the end of the play, Joe says
Keller: (looking at letter in his hand) Then what is this if it isn't telling me? Sure, he was my son. But I think to him they were all my sons. And I guess they were, I guess they were...