From a moral perspective, public policy on abortion in the United States may considered to constitute an unjust law. I will discuss this in the following section. The issue here is the action of individuals to enforce the moral law. Catholic moral teaching sees the individual always within a social context. The human person is a member of society by nature, and rights, obligations and relationships arise from this fact.
Society is ordered toward the common good.
Since morally evil and criminal acts detract from the common good, the question arises whether individual members of the society may defend the common good by individual action. Human society is an ordered society, and an essential part of that order, reflecting both humanity's rational nature and its divine origin, is the power to legislate and to enforce the common good by coercive or punitive action. However, this power is reserved exclusively to the publicly established civil authority. It carries with it the judgment of God and the penalty of excommunication from the Church. In the mind and practice of the Church, these are sufficient signifiers to indicate the mortally serious nature of the sin of abortion.