It's simple: vehemence means higher beta frequencies, and higher frequency means less judgement and more impulse. It was / is good for the fight or flight stage of animal and human evolution, but it takes us away from being in touch with our intellectual and intuitive parts of our minds, which are stronger toward alpha frequencies. Pay attention around to people, on subjects that you're neutral about. You'll notice what I noticed. Also, as we create our reality with our thoughts, emotions, beliefs, and because vehemence arises when negative thoughts, emotions, beliefs dominate, what we create and attract in our realities will be similar thought and physical forms. That's why compassion accompanied by anger and / or hate, however justified do we believe them to be, is bad for us, and everybody.