Just some ideas on what rational action consists of.
When we talk about free will, rational natures etc, all that we require is a responsiveness to reasons. (All though I do not necesserily concede the impossibility of supernatural libertarin free will)
1. From the previous post, Rational action is driven by universalisable maxims.
2. Similar reasons for acting yield similar actions. i.e. Treat like cases alike - The principle of procedural justice. This says nothing as to what are the relevant bits of information that go into how to treat a case.
3. Treat two cases differently only insofar as the two cases are relevantly different. This is the principle of proportionality. We should not treat two slightly different cases very differently from eachother.