SRD said:
"Good" implies altruism, respect for life, and a concern for the dignity of sentient beings. Good characters make personal sacrifices to help others.
"Evil" implies hurting, oppressing, and killing others. Some evil creatures simply have no compassion for others and kill without qualms if doing so is convenient. Others actively pursue evil, killing for sport or out of duty to some evil deity or master.
People who are neutral with respect to good and evil have compunctions against killing the innocent but lack the commitment to make sacrifices to protect or help others. Neutral people are committed to others by personal relationships.
I think, in the D&D sense, being a jerk doesn't qualify you as evil. The defining factor really seems to be whether you are willing to kill 'the innocent.' I would assume that in D&D parlance, innocence equals non-evilness.
So here's the question. If a society has access to detect evil spells, such that most any accusation of "he's evil" can be corroborated without too much trouble, why would the society
not punish people for being evil? If you had proof that someone was not a good person, you would be remiss in your social duty if you did not bring this to the attention of the proper authorities. Those authorities would then look into the person's past, maybe spare a 25 gp divination to see if he had committed any significant crimes, and then assign a punishment.
This punishment could be rehabilitation in enlightened societies (basically a paladin finds a person who is not living up to the moral standards of society, and the community works to solve the person's moral failings), or mild prison sentences in most societies, with exile for repeat offenders.
And consider carefully before you go saying that this would itself be evil. If 'evil' means that you're a killer (which the D&D core rules description of alignment seems to suggest), then this method is similar to either good police work (to find criminals and punish them), or psychological examination (to find potential criminals and rehabilitate them before they hurt someone). And that's something we can all get behind.