It's true that anybody under Islam becomes somewhat pyschotic, but Mohammed essentially designed a "religion" for himself: he was a savage male from a savage tribe that made its living by taking things away from other tribes and peoples around them. One of the "things" it often took was their women, who were then forced to breed with these primitive Arabs.
All Mohammed did in his "religion" was create a legitimizing cult for his tribal behavior. And he himself probably was psychotic, so he took it one step beyond and made it truly savage and awful.