An Objective Basis for the Categorical Imperative

I don't see any reason in principle why subjective morals should be less binding than objective morals.

Correct. We bind ourselves to our own ethical system without regard to whether we can see if it has an objective foundation.

But Kant's meta-ethics derives from the premise that the categorical imperative is objective. That is to say, moral questions are determined without regard to the person asking them or the cultural or temporal context in which those questions are asked. I take this position as well, as I place all such questions as axiomatically derived from what humans demonstrably are-- rational, autonomous, sentient, self-conscious, intentional, with blood and bones, with parents and life spans, and as members of families and tribes. This is the objective foundation of Kant's principle in the Groundwork of the Metaphysic of Morals: "Act only according to that maxim whereby you can at the same time will that it should become a universal law" and "Act in such a way that you treat humanity, whether in your own person or in the person of any other, always at the same time as an end and never merely as a means to an end" and finally "Therefore, every rational being must so act as if he were through his maxim always a legislating member in the universal kingdom of ends."

These principles are of course the basis of the universalism that we see in the Declaration of Independence, the United Nations Charter and in genocide tribunals-- that right is not might and that right has an independent and transcending reality from any given individual but not from humanity generally.