Perhaps this does have something to do with fraternity--that is, a third interesting objection that Luc Brisson raises against Bobonich.
In an earlier post, I had emphasized that, as a matter of method, when one proposes a developmental explanation of some change, it is crucial first to describe that change correctly. The explanandum will not be correct, if the explanans has not first been given correctly.
Bobonich maintains that a crucial change between the Republic and the Laws is that in the former only philosophers can be virtuous and happy, whereas in the latter apparently all citizens can be so.
Now, is this change as great as it appears? One way to argue that it is not, is to suggest that 'virtue' (or 'true virtue') gets used in different senses in the two works. For instance, in the Phaedo (and presumably in the Republic), true virtue is salvific: it liberates the person who has it from cycles of reincarnation. The difference between true and false virtue, is the difference, really, between eternity and transience. Now: does Plato in the Laws come to believe that all citizens in a well-governed city are liberated upon death from cycles of reincarnation? If not, or even if his discussion prescinds from that question, then evidently the meaning of 'true virtue' has changed across the two works, and therefore we cannot yet speak of a change in doctrine (as opposed to emphasis or purpose).
But another way is to argue that the subjects to which virtue is attributable or not differ, so that what appears to be a wider extension of the term really is not so. This is the approach that Brisson takes, thus:
In the Laws, Plato replaces the functional class of producers in the Republic by metics and slaves, responsible for taking care of agricultural and manufacturing labour (5, 741 E) and commercial exchanges (ibid.). There is no money in the city of the Magnesians (5, 742 A-B), and no one must seek to become wealthy (5, 741 E). There can be no place for poverty and wealth (5, 728 E-729 B) in a city that seeks virtue in its totality. One might say, then, that with regard to production and the exchange of wealth, the city of the Laws is much more strict than that of the Republic. Here the economy is completely set aside. In theory, therefore, the Republic is less radical than the Laws, for in the former we find a place for a class of producers who can possess land, a workshop, or a business, who may have a wife and children, and who do not seem subject to any particular constraint. But we must qualify this last assertion, in so far as the producing class is under the domination of the military class, who subject it to constant control (4, 421 D-422A), which would probably not be tender, although practically nothing is said on the subject. Ironically, it seems that the major work of making all citizens happy is done by taking those people who are lower-class citizens in the Republic, and denying them citizenship in the Laws. These people lack happiness, and they still inhabit the territory of the city, but because they are not citizens they are not part of the city (emphasis mine).