Livy has some shocked and highly dissaproving comments on the Bacchanalia, although the accusations raised are stock prejudices that were also levelled against other cults including Christianity. (Its the typical 'babies on the bayonet' tabloid journalism, two thousand years ago). However, it does vividly demonstrate the degree of dissaproval for non-official religious ceremony - in the Religio Romana the gods one worshiped was a matter for the individual and the location, but the rites used to worship them had to be of the standardised, correct and approved form.

A sample:

To their religious performances were added the pleasures of wine and feasting, to allure a greater number of proselytes. When wine, lascivious discourse, night, and the intercourse of the sexes had extinguished every sentiment of modesty, then debaucheries of every kind began to be practiced, as every person found at hand that sort of enjoyment to which he was disposed by the passion predominant in his nature. Nor were they confined to one species of vice---the promiscuous intercourse of free-born men and women; but from this store-house of villainy proceeded false witnesses, counterfeit seals, false evidences, and pretended discoveries. From the same place, too, proceeded poison and secret murders, so that in some cases, not even the bodies could be found for burial. Many of their audacious deeds were brought about by treachery, but most of them by force; it served to conceal the violence, that, on account of the loud shouting, and the noise of drums and cymbals, none of the cries uttered by the persons suffering violence or murder could be heard abroad.

Livy, History of Rome, Book XXXIX

There is a useful article on the Bacchanalia in A Dictionary of Greek and Roman Antiquities.