I don't get it: How can you not see that eating food you don't need to eat is wasting food? If you throw away food, it has been made for nothing and goes to waste. If it hadn't been made, that would have saved resources, and nobody would be worse off.
If you eat food you don't need to eat, same thing: If it hadn't been made, that would have saved resources, and nobody would be worse off. Exactly the same end result: Food was made for no net beneficial end result; resources were wasted.
What's your definition of "waste", that they can be anything but the same thing?
Old people in Japan went through the deprivation of post-war Japan. Not all boomers were raised the same. It is harder for someone who has known famine to accept it is ok to throw food away for fun.
US grandparents think you can buy a house with a part time job, Japanese ones think that you could save a life with a watermelon. Different delusions.
But the irony is of course that in the West most people eat _far_ more calories than they really need, so they are doing basically the same thing.