Ethics should follow the same standard normal distribution model as everything else. Which means that 50% of the population has less than average ethics.
Not everything follows a standard distribution model. In fact, since some psychological tests are designed to return a standard distribution result, if the traits do not occur in the population along a standard distribution, the psychological tests are designed in a way which will give inaccurate results.
Despite being called normal, not as much as you would think follows a normal distributon. But if your main point is that there is some mean value of ethicalness and 50% fall above and below that value then I suppose there's not much to argue about there.
It's also common for more or less than 50% to fall below the median. The average M&M fun size package has 15 M&Ms (mode, median=15; mean=15.02). Only 25.6% have fewer than that. As fumeux_fume stated earlier, not everything follows a normal distribution.
Since morality is socially mediated, I think it's reasonable to hypothesize it would tend to be N-modal.