Even Cicero, the statesman and (sort-of) philosopher was not immune to the delusions and temptations offered by false gods.
By contrast to the pagan depravity, we see in Christian worship the highest virtue held up on display. This is not because of the goodness per se of the people worshiping (though compared to pagan behavior they are quite restrained), but because of the God who is being worshiped. For when pagans enter a church service they see that "either the precepts of the true God are recommended, His miracles narrated, His gifts praised, or His benefits implored." When we declare the Gospel through preaching, praying, and singing we hold out to the world a picture of the God who in Holiness stands opposed to our sinful rebellion. And while visitors today may not be quite the same as their pagan counterparts in the 5th century, I think it's interesting that we do often see that when the Gospel is preached properly "their petulance is either quenched by a sudden change, or is restrained through fear or shame." Some of this no doubt is because of group mentality (when we enter a room full of silent people we're more likely to be silent ourselves, whether Christian, pagan, or other), but some of it is also the overwhelming weight of the Glory of God displayed in the broken Christ on the cross held out to us.
Augustine appeals to the Romans to embrace Christianity and to reject the deceitful wickedness of paganism. In Christ alone is found the solution to the desires of the human heart, and only in the heavenly city do we see the eternal glory that we long for on earth but can never acquire because of our own sinful hearts.