VENIAL OR MORTAL SIN – “SIN IS SIN”

Venial sin becomes mortal because a person ignores his conscience and commits a sin that violates his conscience in a grave way. Cutting yourself off from sanctifying grace and greatly offending God (Catholic.com)

Under the heading “Erroneous Judgment,” the Catechism states, “A human being must always obey the certain judgment of his conscience. If he were deliberately to act against it, he would condemn himself. Yet it can happen that moral conscience remains in ignorance and makes erroneous judgments about acts to be performed or already committed” (1790).