Is baptism a washing away of sin or purely a rite of admission to the Christian Church?

The Holy Sacrament of Baptism –
Before St Augustine, Baptism was received by adults as a rite of admission to Christianity and there is no mention in the Bible of Original sin.

Progressive theologians think St Augustine was mistaken to teach that all babies inherit Adam and Eve’s sin by having been conceived in lust.  Rev. Cauley says: “There is no greater threat to Christianity than the doctrine of Original sin”… 

Vulnerable Young
Branding infants sinful when they have done no wrong seems perverse. Negative labels can be spiritually and mentally damaging.  Unjustified shame of sinfulness may be deepened by having children proclaim faux transgressions, as in Penitential prayer recitals.  Are our youngsters made more susceptible to being abused by  bearing the disgrace of unmerited sins?