"Why do humans seem to be so unable to rule themselves."
I read in that question, the unstated premise that human society should be problem free, that conditions should be able to be perfect. So let me ask you another question to perhaps highlight that your thinking may be clouded by a false premise that you have accepted without question:
What makes you think that things are supposed to be perfect? Who implanted that idea in your head?
It is only natural and normal for human society to have problems and conflicts to varying degrees given the individual difference that exist from one person to another. Conflict is a normal and natural occurrence. It happens within all other species. Why do you think humans should be exempt?
I will submit to you that the expectation that things should be perfect is borne of religious indoctrination. The JW teaching that man was created perfect in the image of God and problems are the result of man's fall into sin, creates the false idea that the conflicts and problems we face as humans are somehow unnatural and we are a failure as humans if we're unable to permanently end all conflict.