Thank you for your deep investigation of Ciceros critics, especially about Epicurean justice.
In this subject the Stoics often seems to have the "better ethics" because they emphasize cosmopolitism, altruism, philantropy for all humans, not only friends.
As a defense I only know 2 aspects:
- Injustice leads to disturbance ( guilty conscience, fear of being discovered )
(both not the strongest arguments I think, see platons ring of gyges which makes invisible )
- The Epicurean Sage only pursues natural/necessary desires and there is no need for injustice because these are easy to optain and no one must be harmed.
( But what when in extreme situations, even they are not fulfilled ? )
What I miss is that doing good feels good, reduces stress and sociability is part of human nature (the Stoic had there oikeiosis, I heared Hermachus took over parts of it. But here is a stronger point for Epicureans to emphasize (social) feelings)
So that it is a natural/necessary desire (compassiong, charity) to do good things and to get pleasure from it.
Or maybe that is in the virtue of friendship ?
That justice is limited to strangers and there a limit in doing good being benevolent makes sense to protect from harm from strangers ?
And Friendship/Kindness is for all worthy of it ?
Seneca says of the Stoics this, ( how far goes it in Epicurean Philosophy ? )
‘"No school has more goodness and gentleness; none has more love for human beings, nor more attention to the common good. The goal which it assigns to us is to be useful, to help others, and to take care, not only of ourselves, but of everyone in general and of each one in particular’ (On Clemency 3.3). "
Have all a good and pleasant transition into the New Year