if morality were dictated to rational agents through an external source, we could not be sure of its objectivity (i.e., universal and necessary validity). Moreover, the notion of an external source that dictates morality conflicts with our being free moral agents. Hence we must legislate ourselves through our own faculty of reason such that the moral law holds objectively for rational agents such as us.

I agree with everything here until the “must” of the last sentence, as it seems to be based on the implication that said free agents care. There are people who do not care for their own wellbeing, or the wellbeing of others. On a subjective basis, they lack the values that objective reasoning would be built on.

To them that “must” is meaningless. Or worse, they view statements such as that as being dictated to them from an external source.

On top of that, we aren’t completely rational, or able to make completely rational conclusions at all times. We can make attempts, sure. But we have biases, we fall into fallacies without realizing, and like I said some of us just don’t care.

Morality can’t be objective if we can’t be objective.

but I’d rather not recapitulate the entire work. If you’re interested, I would read the following entry page on the issue.

I understand not wanting to do that, so all good.

Though. I’m more interested in a discussion than anything else.