Casting spells with subtypes.

[Cabral]

But accepting the fact that D&D is a game with alignment, it just bugs me that you cannot, for example, play a "good" necromancer.

It's a little hard to escape the idea that graverobbing is not a good act. That said,

1) That stems from the default campaign setting's assumption that (almost) all undead are evil. If your campaign changes that, then the descriptors on the spells should change to match.

2) Eberron/Book of Exalted Deeds has a work around where Undead remain, by and large, evil, but you can play a good "Necromancer". Instead of creating Undead, you create Deathless. Deathless are like Undead, but are motivated by Positive Energy, not Negative Energy. In addition, while you are still animated corpses, creating Deathless has more in common with summoning a Planar Ally (substituting a soul that has passed on for an outsider) than creating Undead.