I remember learning about the difference between major and minor in music class as a kid with the teacher saying that major sounds "happy" and minor sounds "sad"... But most of the sadder songs that I can think of are in major?
if you actually write a 'sad' song in a 'sad' key, then the entire song actually is sad and makes you feel sad. it turns out that's not what most people really want, so it's more common to do it in a major key so it makes you feel good about a sad thing. that's something that i think almost anyone could be on board for