The plane of existence where they are located is very low, and the lower levels are dominated by chaos. Chaos, by its very nature, can generate anything, both positive and negative. When one is connected to these planes, it is very easy to self-destruct, as the yehuborim do here.
The war they wage is on the level of perception. Their power is based on this, because the Gods are actually on a higher level. Over time, they have stolen concepts from other cultures, modified them, and made them evil.
In some ramifications, they present the universe itself as evil, and how people should hate it and defend themselves against it, with the result of sinking into the deepest layers of chaos and leading humanity to a deadly degeneration.