Why is Chernabog considered evil? All he does is to throw around some demons and souls, and the souls at least went to him willingly. I mean, sure he is a jerk, but at worst he is some kind of bully, not the incarnation of evil everyone seems to want him to be. Even House of Mouse seems to interpret him that way (as a bully, not as a "Satan"). It seems as though the only reason he is an evil being is because he looks like a demon, which is roughly as morally decent as claiming someone is evil because they have black hair.
That's exactly it: Chernabog is a bully. He's bored, petty, and uncaring. He takes the demons and souls that came to him, changes their forms at will, and compels them to dance for his pleasure. They may have come to him willingly, but they clearly have no control over what Chernabog does to them once they get there. That's a pretty vivid interpretation of Hell: to be stripped of your free will and turned into simply the Devil's plaything.
Which idiot decided that Beethoven's Symphony Number 5 was an "abstract" piece of music? It very distinctly tells a story, that of Fate (the famous opening theme) versus the Hero (the counter-melody). Even the animation (two tiny white butterflies fleeing from a mass of black ones) reflects this. I can forgive the original Fantasia for using Toccata and Fugue in D Minor since Bach obviously didn't foresee his work being used as the theme music for the quintessential Mad Scientist but this just smack of laziness.
Complaints like this were addressed by the creators, when fans were upset that some of the pieces of music had nothing to do with the actual "stories" (the Nutcracker Suite featuring no characters from the ballet from which is is adapted, for instance). They said that their goal was to animate the "impressions" they got from the pieces, separated from the context of the songs. As one animator put it: "We say that The Rite of Spring makes us think of dinosaurs. So prove that it doesn't!"
There is some justification for it from a musical standpoint, actually. The 5th doesn't have a melody the way most other pieces of music from its time had. The 'melody' is clearly made of layers of the famous 'three quarter notes, HALF NOOOOOTE' line, and the counter-melody has aspects of it as well. In that respect, it is like an abstract painting, which is all about playing with form without content or subject. Still, the fact that it still has two discernible threads attests to Beethoven's awesomeness, and the dubiousness of their choice.
Keep in mind, the fifth was not program music. Beethoven himself never stated his intent for his themes in the 5th. The story that it's about fate came from his assistant, not from the composer himself. Also the animators on the original depicted exactly what Pastoral's third and forth were meant to convey - an outdoor party which gets interrupted by a thunderstorm.