Toon is absolutely right and his history lesson is on the mark re the Pistevo. His notions about koinonia are distincly Western and do not express the Orthodox, read Greek here...it is one of our words, phronema.
Rendering "Credo" as "We believe", as Benedict (pre elevation) said, is not heretical.
Insidious western individualism is heretical and lies at the root of the "dictatorship of relativism", to use another phrase of Benedict's. This dictatorship is directly responsable for the advancement of such abominations as the gay "marriage" and non-celibate gay ordination agenda.
Historically, the Nicene-Constantinopolitan Creed was developed to combat heresy. While not historically correct to render "Credo" in the plural, it is essential in this period of history if the Creed is to fulfill its proper role in attacking all that would undermine the community of the Body of Christ.