And don't assume that even if the Living Saints are the Emperor's version of Daemons that it makes them in any way positive. He's the corpse-god of mankind, the end result of ten millennia of fanaticism, superstition, dictatorial rule and xenocide as the state religion. All magnified by the psychic backwash of thousands of psykers slowly burning to death in the Astronomicon.

It's a running theme in the warp that any emotion, when taken too far, leads to Chaos. Khorne is the god of Honour and Glory, Slannesh is Love incarnate, Nurgle has a decent claim at being the personification of happiness. All of these things, taken too far, end up in a bad place.

Tzeentch? He's the God of Hope, the wish that things were different.