To what kind of moral theory does robertson appeal to support his notion of procreative liberty?

The answer to this question is the Kantian moral theory
The Kantian moral theory refers to the standard of what's considered good and bad that's not depending on the consequences but rather based on whether the actions served its purpose.
For example, under Kantian Moral theory, Killing other people would be justifiable if its being done for the Glory of our own people.