First and foremost, it should be noted that no set of ideas – be they religious, social, or political – is immune to extremism. Any ideology or tradition can be corrupted and become destructive once the wrong kind of people or circumstances take over. But it’s also true that some beliefs are more prone to generate fanaticism and intolerance than others. And that’s where the case is made that, although both can become dark and dangerous, Christianity and Roman polytheism are not equally (in)tolerant. In fact, I’d argue that the latter has a greater potential for tolerance than the former and indeed was more respectful of other gods than Christianity ever was and is.
As pointed out, Roman polytheism was not exclusivist and accepted the existence and integration of non-Roman gods. A clear expression of that idea is the Evocatio or the ritual by which the deity of an enemy city was invited to switch sides and support the Roman attackers. The Dioscuri were said to have come to Rome thus, though it may only be a legend, but Vortumnus and Juno Regina may have been integrated in the patheon through that ritual, in 264 BCE and 396 BCE, respectively. Romans also believed that other people’s gods were real by seeing Them as different versions of their own. An example that probably mixed that notion with the Evocatio is the case of Juno Caelestis, with Whom the Punic Tanit was identified and “taken” to a temple in Rome after the fall of Carthage in 146 BCE. And Julius Caesar’s take on the Gallic gods or Tacitus’ on the Germanic are well known. There were several reasons to assume an identity between foreign and native deities: political, because it helped integrating conquered peoples; theological, since it allowed Romans to make sense of the diversity of deities and a growing universal nature. Yet monism or syncretism were not a compulsory belief, so there were also openly foreign deities being worshipped in Rome (or its outskirts). Isis is a prime example of that, as is Cybele, Epona, and Mithras.
Yet, if Romans respected and took in deities from other cultures and nations, they could also be intolerant, starting with the elites, who were proud of their identity and sometimes overly so. They could look with suspicion to foreign cults, especially if it endangered traditional orthopraxy and risked breaking the Pax Deorum. And the masses would join in times of war or crisis, seeking someone to blame. But perhaps the greatest reason was the disturbance of public and social order. Or, in other words, religious cults were generally tolerated unless they endangered the status quo or broke the law. And these limits were negotiable to a degree, both in the name of peace and respect for the foreign deities’ orthopraxy.
An excellent example of that is the case of the great goddess Cybele or Magna Mater. Her cult was introduced in Rome from modern-day Turkey sometime in the beginning of the 3rd century BCE (traditionally during the second Punic War). Initial enthusiasm was eventually replaced by shock when Romans became aware of Anatolian cult practices, namely castration and flagellation. The solution was a compromise which prohibited citizens from being priests of Cybele and limited public celebrations. This allowed preservation of traditional ritual within physical and legal limits and without breaking social morality. Isis too had Her temple in Rome, though Her cult had her ups and downs: after Republican acceptance, it was censured in the early imperial period by Augustus, before ascending again and eventually having several emperors among its practitioners. And then there was the Bacchanalia, prohibited by the Senate in 186 BCE after it threatened the social status quo and public order.
The common link in these examples of persecution and limits on religious freedom is that none of them was motivated by religious doctrine or accusations of heresy. Heterodoxy could not have existed because there was no orthodoxy to break in the first place. Nor was there any exclusivist claim determining that all non-Romans gods were false or evil. Bacchus continued to be worshiped, as did Cybele and Isis, and even reached new levels of popularity. Political and social stability, as well as law and order, were generally the criteria by which a cult was deemed illegal or not. Which is why Christians were a problem: because they refused to take part in the established order and actively saught to convert as many as possible, they were seen as threats to both the human and divine peace.
Now, this doesn’t make their persecution any less condemnable, but it does help to understand that the problem was not doctrinal. Or rather it was, but on the part of Christianity, which, unlike Roman polytheism, is dogmatic and exclusivist, and that is what tells us where the greater potential for intolerance is. Ask yourselves: while Romans invited and accepted foreign gods for centuries, how many non-Christian deities were worshipped or tolerated by Christians? Which is the “hardly a tolerant, inclusive, pluralistic, and gentle religious option”? The one that doesn’t claim a monopoly of truth and divinity and has no orthodoxy, accepting the existence, benevolence, and cults of other gods? Or an exclusivist and dogmatic religion that sees all deities other than its own as evil or false and their worshipers as heretics or lost souls in need of conversion?
Michael Bird may never have considered these questions. Then again, he seems to be a very Christ-centred person, which probably makes it harder for him to look beyond the experience and dogmas of his religion.