Because you are viewing a picture and evil as defined by religion is "bad"-- this characteristic must therefore be manifestered on screen either through bad acts or bad/ugly images. It confuses when the conflicting sides share an image that is likable. In movies where the "bad guy" wins or the viewer roots for their victory, one can see that the image of said bad guy is more often than not, similar to that the good guy. In any case, it is a cultural thing and it is now an accepted and expected thing for evil to depicted as ugly/dark.Everywhere you see movies about satan and demons they are pictured as extremely UGLY! Why? Why is a different opinion other than god's so terrible and disgusting to look at?