The Measure of Better
It is a very difficult thing to remember that the average person is of average intellect. What's more, there are many people who are actually below average. This means that the majority of all people are of average intelligence or below. These little details lead eventually to a frightful place.
We tend to live with the concept of Equal Under the Law. Most people end up translating this as all people being equal in general. You'll note that the first paragraph suggests otherwise. Still, we all agree to place this game and, with few exceptions, maintain that all are the same.
Once we acknowledge that some are "better" than others then we have to establish some way of measuring this condition. No one wants to be in one of the lesser categories. All animals, humans included, want to assure the survival of themselves and their kind. If I get to establish the criteria for what is better, I will make it match me and those others I want to protect. This applies to most other people as well.
That does not seem to be the best way to establish a concept of "better-ness" in a human world. No one can be trusted to establish the criteria, or even to apply the criteria, in a fair and just way. Ultimately, this is why we cannot make such distinctions official.
Instead, we use the free market concept. The idea is that those who really are "better" will do better in life and those who are lesser will not do as well. This makes the true measure a matter for natural selection. Those who are better at surviving, from Nature's point of view, will do better. The human herds fluctuate with different dynasties coming and going.
If we keep this in mind, we will ultimately find that the measure of "better" is not what we might think of it as being. It is not necessarily intelligence. It is not necessarily physical toughness. It is instead the ability to lead the herd into circumstances that benefit the leader and the leader's family. Of course, it helps the long term survival if the leader can also lead the herd to fertile pastures.
So, it may be a matter of great frustration that there are people of wildly varying levels of intellectual complexity, but we still choose to put up with the system. We let nature take its course and hope that our children will be better leaders than we. Besides, when you consider that most people consider them selves to be in the above average category, would you really want to be officially tested and categorized?