Prisons and Welfare have the same general purpose, the regulation of the poor; so if one is "generous" the other is also. But Justin used the word to mean merely "large", I think.
An externally-unthreatened state (viz., the Empire) could direct more of its energies toward regulating its constituents; moreover, without external enemies, it would be harder to distract dissident internal forces from resisting and attacking the state structure, especially the leadership, so they would have important reasons for exerting surveillance and control.
I think we have quite a different situation coming up than what was observed in the past, when capitalist states could vent surplus production on war and imperialism. The imperium is nearly complete; many there are alive today who will see Coca-Cola, Mickey Mouse and Honda prevail in Parthia as in Peoria.
-- Gordon