Rationalist means you begin with principles that look self-evident and you deduce from there.
And, Locke is part of this rationalist position, which includes Hobbes and goes on to Rousseau and Kant. It is a tradition which sees political theory as being something very much like mathematics. You begin with axioms that look self-evident; and then you can get to universal truths just like they thought Euclid's geometry works.
You can get to universal truths that then apply – that they are true and good for all political times and places; for human beings in every single time and place in all of human history and around the globe. So, I have a problem with that entire non-empirical approach to begin with.
But, in particular, if we take a look at what did they do with it, Locke begins the Second Treatise of Government with a number of assertions – they are really axioms, like in a mathematical system.
First, that human beings can access universal eternal truths for all times and places through individual reason alone, which he says "teaches all mankind who will but consult it."
Second, that all human beings are intrinsically perfectly free and perfectly equal, he says.
And third, that it's only by the consent of the individual that they become members of any political society and thereby incur moral obligations.
Now, these three axioms are the basis for – I think for most of what today is referred to as liberalism, both for Progressive Liberalism and what today is called Classical Liberalism. And I think that the problem is that these three axioms are, arguably, not true.
...the claim that political obligation arises exclusively through choice – well, there's no evidence for that.
If you have a good empirical theory of how do human beings, what is it that brings human beings to take on obligation and to cohere – that is John Stuart Mill's word – to create cohesive families, tribes, and nations – what is it that causes that? How do you encourage that? What's good about it? What's bad about it?
Once you have a good theory of that, then you are perfectly free to come along and say, "Well, look, I think that a cohesive society would be better off if people were treated as though they were perfectly free and perfectly equal." But that's a completely different argument already. But that's not the argument that the Lockean tradition is making.