I think the "evil" descriptor is there in order to clearly establish what is "good" and what is "evil".
While there are still grey areas, which are not so easy to clear, this at least gives some form of constant framework. Magic seems to distinguish between some form of values which we have arbitrarily called these names (see items that work differently for different alignments).
Which is explained with a moderate amount of handwavium, and the fact that in the D&D multiverse, gods are real, and so are devils, angels, demons etc. The powers of Good and Evil have their own dimensions, they affect the world much like gravity or electromagnetism; it's not just a matter of moral ambiguity when your fully quantised Good/Evil binary state can be determined by any passing Paladin.
Philosophically however, I think the alignment system is utter garbage.
On a related note, how about playing a Summoner whose Eidolon has an Undead Appearance? There's nothing in the rules about any alignment requirements to do this, and it would make for an interesting character - instead of a Necromancer who's animating an army of corpses, you could play a character with a single (but increasingly powerful, as you level up) undead bodyguard.
Heck, if the GM could be persuaded to allow some minor tinkering, you could even replace the Summon Monster spells and related powers from the vanilla Summoner class, with equivalent Summon Undead spells. (Normally, Summon Undead has the Evil descriptor, just like Animate etc. - but if you wanted to stick to Hal's suggestion of using undead animals, and the GM is willing to permit it, you might be able to impose a restriction on the spell that makes it non-Evil, but you can only summon undead animals.)
PS: Hello, @Nick T. Vegan! Welcome to the site.