I've heard this theory for years, and it's always bugged me. I do think it's true some of the time, perhaps even a lot of the time. But not all the time. If that's our only go-to explanation, it risks reducing vital social criticism of systemic ills to personal psychological traits. I am hurt and saddened by senseless violence. This doesn't mean that I harbor violent impulses and hate that part of myself. From that angle, we'd never have any collective action, because everything would be seen as individual and personal. In the larger sense, I do see myself as part of a collective human psyche whose violent parts I don't like, but it's not as simple as 1:1 projection of my own individual rejected attributes.