Objective evil doesn't really cover all the bases for me, that's why I'm using theological evil, because the gods can become more evil than mortals and usually precede them down the path by a large spans in time and space. Objective evil sounds more like a "force of nature" but I don't like a world view where lions are branded evil or Evil because they slaughter cute, innocent, herbivores for a living...
I like the fine razor thin line people can walk to be considered neutral while doing evil acts, instead of some referee handing out black cards that stick for life for killing one little innocent, or setting fire to an orphanage. The HUGE grey area between exemplary Good and Iconic Evil (I like this descriptor MUCH better than objective Evil) should exist, because it is real! There are no referees in the real world that say: "sorry but you crossed the Evil limit so now you have a detect evil bull's eye painted on your back for paladins to pick on."
The only time I'd use objective evil is when dealing with sociopathic, pathological serial rapist/ murderers that somehow got stuck with a faulty brain subroutine simply exploiting weak targets in any way they can. That is objective and still not iconic evil since they are not REALLY getting what they want (serial killers generally admit that after the first few kills, the feeling of satisfaction disappears more quickly, not returning after every predation)
Iconic Evil is the total bad ass evil portrayed in fiction: such as Sauron and his ilk. They are obsessed by obtaining more power, more influence, more stuff, continually. Greed incarnated; they stand for anything that is bad. They stop at nothing to gain ultimate power and control and the lack of scruples and their indiscriminate use of violence, intimidation, magic power, and lies and betrayal is the culmination of behavioral evil inflicted upon the general populace. Notice how the general populace gets mauled, but that is how evil works. More for less and thus less for more. This doesn't imply any culture or race, since evil isn't concerned with that ( unless it is using your culture or race to keep you occupied with something else instead of dealing with the real issue). Evil is concerned only with itself.
The quantification of evil; for use in a system in a fantasy environment, is fairly easy, or so I think. It is of course up to the individual GM to draw the line somewhere, but in the grey area he has to step in and say X amount of corruption points, or Y years of behavioral evil, or belonging to Z religion, or being classified as a demon, undead, evil magician/ mentalist is when a detect Evil spell will register you as faint, minor, lesser, major, greater, total evil. Easy peasy! Nothing more, nothing less.