A small addendum to
Wuukiee’s and
arkaem’s w/u’s.
Succubi were indeed often considered to be manifestations of hags. This was not, however, always considered negative. The resistances to the witching world in general, including the old-evil-ugly witch stereotype, stemmed from Christianity’s fight to gain control of the European people’s beliefs. Christianity was a religion that rejected passion, while many of the ancient religions embraced it (at least the Dionysian ones). The most apparent example of this is the portrayed character of the devil in Christian religious art – the man with the goat’s hooves is of course the ancient god Pan.
The Hag character is a personification of a witch/fertility goddess. The act of having sex with a fertility spirit is obviously considered negative by a religion rejecting both spirits and sex.
As Tiefling correctly pointed out to me, the succubus as an evil spirit interpretation does not necessarily belong to the Christian church. It’s more an image that they took a ride on. The dark side of mythical entities in general cannot be ascribed to Christianity; Nature, passion and other such worshipped elements weren’t considered necessarily good in any way – they simply weren’t all bad.