Participating in Public Rituals in the Roman Empire

This goes against what I thought I knew about the sociological implications of refusing to partake in public sacrifices in cities of the Roman Empire:

Normally in ancient towns there was no obligation to take part in public rituals. A glance at the dimensions of the buildings here large-scale public festivities were held makes clear that the entire population cannot possibly have take part in such celebrations. The first explicit requirement to take part in public worship, and obligation that was truly enforced and sanctioned, is to be found in Traianus Decius’ Edict of autumn/winter AD 249, at the time of the first extensive and official persecution of the Christians. Until then, no one was bound either to sacrifice or to take part in public rituals. Finally, there is plenty of good evidence for consciously cynical or indifferent attitudes toward the gods, and towards religious cult. Such views can be found in works by convinced atheists and the adherents of philosophies, such as Cynicism or Epicureanism, that denied the existence of the gods or questioned their ability to act in this world.
— Jörg Rüpke, Religion of the Romans, 7-8

I can't defend or challenge this argument, but it is different from what I thought I knew.