Religion in ancient Rome
Imported mystery religions, which offered initiates salvation in the afterlife, were a matter of personal choice for an individual, practiced in addition to carrying on one's family rites and participating in public religion. The mysteries, however, involved exclusive oaths and secrecy, conditions that conservative Romans viewed with suspicion as characteristic of "magic", conspiratorial (coniuratio), or subversive activity. Sporadic and sometimes brutal attempts were made to suppress religionists who seemed to threaten traditional morality and unity, as with the senate's efforts to restrict the Bacchanals in 186 BC.

Q: What did the mysteries seem to threaten that made the Romans occasionally attempt to ban them?
morality and unity