Although beliefs can support each other, they cannot justify each other as at some point a belief must be anchored to reality in order for a belief structure to have any merit at all.
Take religious beliefs for instance. Examining a religious belief is like peeling an onion: after stripping layer after layer there is absolutely nothing at their core. Although some folks simply claim that they “know” that such beliefs are absolutely true – e.g., that a god exists – we can do little but take their word for it as they are unable to clarify what they mean by this assumption.
Not only can they not be substantiated – other than through some irrational leap of faith – they are often self-destructive, when they become weaponized in the struggle between competing religious factions in order to attain absolute dominance. As a result, religious beliefs continue to be a major cause of death and destruction on our world, from our distant past to the present moment.