Ethical and Nonethical: Why only two options?

There is a common tendency among people to move everything or to adjust everything (and everyone) towards the mean (or is it the central tendency?). What it means is that people on the superior half do not get appreciated as they should be in an absolute manner and people on the other (inferior) half get unnecessary sympathy.
The point that i m trying to make is in reaction to some of the questions that i have confronted recently. The quality that i m talking about is the morals and ethics being practiced by people.
Qualities/attributes/performance are generally measured in a relative sense, a person's wealth (rich and poor), knowledge ("he is more knowledgeable than me"), class performance (ranks) and so on and so forth. But when it comes to ethics and moral values people generally tend to make judgment in a more absolute sense rather than relatively. Not even Lord Ram was sparred in this regard (yes, i m talking about the "agni-parikhsa" of Maa Sita).
So, why this bias? The answer to me lies in the same old central tendency and even more in the tendency of human beings to "pull" or downplay others' qualities so as to justify one's inability to stick to the right path.
When it has been generally agreed upon that attaining 100% in any measurement is close to impossible (one of my learnings from MBA) then why do we try to impose 100% compliance in ethical behavior. People generally try to find out that one-off incident/instance to totally negate a certain person's otherwise "morally/ethically" commendable behavior. But why this discrete function of ones and zeros, we are humans not machines! Can't we assign a percentage rating to the level of ethical soundness.
[THIS POST NEEDS SERIOUS REVIEW AND I'LL BE BACK WITH A MORE THOROUGH AND ELABORATE POST]

PS: Comment is a scarce commodity here, so every kind of it is welcome :)