Slay Living is the opposite (I believe) of Raise Dead or Resurrection or something like that...basically the complete opposite of a clerical restore-life spell.
So if Slay Living has the [Evil] descriptor than Resurrection should have the [Good] descriptor since it's doing the opposite thing.
Inflict spells should be Evil, Cure spells shuold be Good. Since they effectively tap the same energies and do the same thing.
Spells that inflict diseases are evil, spells that remove them are good.
There's nothing WRONG with this, per se. But the default, and the assumption I like best, is that curing and killing are not in and of themselves of any particular alignment or origin. Death and Life are neutral forces...one can be good and work for Death, or Evil and work for Life (imagine a growing substance of wickedness that regenerates, and an opposed crusader wielding negative energy against it...kinda like radiation vs. a tumor).
Like any other tool, they can be used for either end...but killing the wicked king outright is arguably LESS evil than bashing his head in until he bleeds to death.
It's because they're morally gray that they're not absolutely one alignment.
Summoning a fiend, on the other hand...or warping someone's soul into a shambling servant...those things turn you wicked just by doin' 'em.