Defect in Immanuel Kant's idea of Rights

There is a tendency to attribute so much of importance to Kant's contribution to the idea of universal human right. No doubt Kant did contribute to the idea of human right, but I do think there is an history that goes beyond Kant why the concept of universal human right so emerged. I shall, however, not delve into that part for now. Kant believes that every human person is worthy of respect. His idea of worth of a person is derived from the fact that we human are rational beings. 

Jeremy Bentham argued that pleasure and pain are our sovereign masters. And so in Bentham's moral philosophy, what ought to be done is governed by this preference for pleasure and our dislike for pain. Bentham thus considered the idea of natural right as 'nonsense upon stilts'. Kant disagreed. Kant argued that we like pleasure and dislike pain, yet we are also governed by reason.And this capacity to reason gives an individual that worth, and so the right. Kant's ground for right thus is grounded on individual's capacity to reason.

But is Kant's idea well grounded for human right? I don't think so. If an individual's worth is based on her rational faculty then those individual's whose minds are blank have to be considered as devoid of any worth. This would leave out children who are not yet able to think rationally think or those aged human persons whose mind is now vegetable or even those who are in coma. Kant did give so much of respect for a human person. He went to the extent of arguing that we are to treat human person as end in themselves, and never as a mean to some end. However, had he provided a more sturdy grounding for the worth of a human person that can include all human beings, his overall argument about the idea of right would have gained more coherency.