I'm with the dude above....in D&D, [evil] and [good] and [law] and [chaos] (the spell descriptors) are tangible forces.
Calling a spell [evil] just means that it's run, governed, powered, and watched over by the evil energy in the world. It taps the very power of evil to do it's work.
It's up to the DM to make evil spells seem harmful and destructive. Giving somebody a negative level may not be directly evil, but watching "their skin drawn tightly over their bones, moaning in agony as claws of blackness race under their skin and tear at their very soul" may be a bit more wicked.
They're just tangible forces.
Of course, the rules don't say it affects alignment, right? They just give that definition to spells, but the spells don't determine what kind of alignment you can be, or if it starts to sway you. That's why alignments are so loose now. You can wound somebody's soul with the power of evil, and still not be evil yourself. That said, Pelor won't be giving it to you, and he won't let you summon fiendish hawks, either. Not because you can't use 'em potentially for good, but because they create a bit of a gateway, of sorts, a path that evil can walk again. Keeping those spells from being cast is much more important in the long run than any benefit they may yield (which may, in the end, be perverted to evil anyway).