To be sure this does not stipulate that all actors be selfish, merely that no penalty should inhibit selfishness.
That is completely false, you are simply attacking the straw men that 100 years of oversimplified critics of classical liberalism have set up.
The classical liberal tradition always had a strong association and interest in English Common Law and never asserted individual action is above the law, exactly the opposite is the case. The Law very foundation that classical liberal build on.
That's why there is a whole field of economics called 'Economics & Law' that goes back a long time.
> To be sure this does not stipulate that all actors be selfish, merely that no penalty should inhibit selfishness.
The factor that inhibits selfishness is the law. But you are correct, no classical liberal thinker thought people should be punished for being selfish in of itself.
I suggest you quickly take that up with the wikipedia page and several texts then.
https://en.wikipedia.org/wiki/Classical_liberalism
Evolution of core beliefs
Drawing on ideas of Adam Smith, classical liberals believed that it is in the common interest that all individuals be able to secure their own economic self-interest.
What you said is:
> A core classic liberal belief, arguably the core belief, is that nothing should stand in the way of individuals being able to secure their own economic self-interest.
You literally said 'nothing'.
It is of course true that they believed that self-interested individuals seeking voluntary trade to improve their self interest within a legal framework would be beneficial for society.
Note how Adam Smith never says 'its amazing to steal as much money as possible because following your self interest is good for society'.
I suggest you read Adam Smiths actual work, The Theory of Moral Sentiments.