Assuming a bright line dichotomy between human and animal, there are two ways to understand his statement.
- Either he meant that only those few that understand Quantum Mechanics are truly human, and he thereby cruelly consigns more than ninety nine percent of mankind to a less-than-human state,
- or he meant that although the uninformed masses are human, those who understand Quantum Mechanics are vastly superior to them.
Even further: if you don't understand Quantum Mechanics, your world view is not merely deficient, it is delusional. Your view of reality is not just imperfect- it is false.
If you think you understand the basic truths of existence when you do not, if you merely skate along the two dimensional surface of the empirical evidence that can be perceived by the uneducated mind, then you have failed to fulfill the specific function of humanity, which is to comprehend truth. You are certainly less sapient; perhaps you are less than sapient.
I don't think that Dr. Gell-Mann would say that the poor uneducated masses are less entitled to life, or that they don't deserve our love. Although he is, nebach, a proud atheist, (whose incurable drive to assert his superiority and to demean any possible rival makes it impossible for him to recognize a Ribono shel Olam, as becomes obvious after watching this or reading this,) he is not, God forbid, a Nazi. But he understands that Quantum Mechanics is so important, so essential, so fundamental to the meaning of reality, that those who fail to understand it are lesser beings, just as great apes are less than humans.
Also, I think that it is misleading to define "human-ness" exclusively on the basis of rationality. There is a moral component as well. I'm sure there are people who are conversant in Quantum Mechanics who are no better than those gentle giants of the jungle.