Human reasoning as a Way of Knowing is a particularly interesting characteristic of the human intellect because people, by nature, are able to think intuitively, without restraint and in such a way that a primary piece of information can be processed through reasoning to gain further understanding. In this way, people are capable of acquiring knowledge by compiling a number of facts, interpreting them and of course by way of reasoning, finding them to be true or not true'. In short, reasoning can be defined as any process which involves drawing a conclusion from a set of premises.
That's the difference between a human brain and a computer. You often hear people say that a human's brain is much faster than a computer, but that's not true at all.
Does a human's brain smarter than a computer? The answer is yes. However, a computer is a lot faster and it has the capacity to search up to 3.5 to 4 billion ops per second, while a human's brain on the other end, can only do a maximum of 500 ops per sec.
A computer barely makes mistakes because it uses algorithms method to draw its conclusions. With that says; if the result comes back with mistakes, the mistakes were made in the algorithm process (input, process, and output). While on the other side, a human brain makes a lot of mistakes per second, which leads to our brain's ability to be creative and uses reason to draw better conclusions.
However, despite the fact that our brain is a lot smarter than any computer; the strength of basing an ethic entirely on human reasoning is somewhat limited due to the fact that human reasoning is not the only way for us to get more in-depth information or knowledge.
Also, as human, we're naturally biased. Bias by definition is showing prejudice in favor or against someone.
So this would give room for more bias judgments, decisions, or conclusions.
There are also; motion, feeling, languages, perception, faith, etc. which are very essential in making accurate judgment or conclusion. So since we don’t know it all as human, the flaw of basing an ethic on our own reasoning automatically points out its limits as well as its strengths.
As a result, there would be disagreements because some people would over benefit from such an ethic, while others would under benefit from it; which automatically create an imbalance.
And of course, wherever imbalances take place, anger and frustration will later come knocking at that door. With that says; regardless of how intelligent one can be, no one knows it all and psychologically speaking, there's no such thing "The Absolute Truth" because subjectivity is all around you.