This old idea has flaws... firstly, the idea of anger in the series only applies to the Saiyans. And even then it's not consistent - only Gohan becomes more POWERFUL by being angry. Vegeta just uses up all his ki recklessly. It's not the same thing, and it often costs Vegeta the fight anyway. Vegeta loses his self-control, he doesn't become stronger.
For other characters, anger means nothing. Frieza was positively enraged when things didn't go his way, but that didn't make him stronger Gohan-style, it just made his defeat more humiliating. Anger didn't help Cell, anger didn't help the young Mirai Trunks and Mirai Gohan against the Androids (or any of the future Z Fighters, for that matter). In the Majin Buu saga, everybody who got angry at Buu was eaten, killed or absorbed - Dabura, Vegeta, Gotenks - yet the one who knocked Super Buu around like a pinball, Mystic Gohan, did it by being completely calm and confident. Doesn't that go against the whole concept of anger?
Anger and a sense of loss pushes Saiyans into their super forms. It doesn't make anybody stronger except for Gohan, and Gohan reached his full potential by letting that anger go.