IMC, I solve the
[EVIL] vs.
cuddly l'il evil dichotomy in a number of ways.
If you are born on (take your first breath on) an [Evil] plane, your soul is Tainted. This is tough to lift. You probably gain the [Evil] descriptor.
If you are born on the Prime, your soul is Natural. You are not necessarily [Good] or [Evil].
If you have a fiendish parent, you gain some powers (some of them will be [Evil] powers, probably -- poison, animate dead, smite good). You don't necessarily gain the [Evil] descriptor.
If you voluntarily draw power from an [Evil] being via worship, you gain the [Evil] descriptor. Clerics, Blackguards, etc. If you atain powerful blessings from a [Good] being via worship, you gain the [Good] descriptor.
If you cast a lot of [Evil] spells (or use a lot of [Evil] spell-like abilities), you will start to gain the [Evil] descriptor.
Detect good, evil, etc. detect the descriptors. Additionally,
detect evil detects undead, and
detect good detects living creatures. Neither would detect a Modron.
Otherwise, you're basically Neutral.
-- N