The USCCB Pro-Life Secretariat has prepared a fairly exhaustive document tracing Christian opposition to abortion throughout history with discussion of ideas about ensoulment. The document ends with a strong note on the primacy of the right to life:
"Given the scientific fact that a human life begins at conception, the only moral norm needed to understand the Church’s opposition to abortion is the principle that each and every human life has inherent dignity, and thus must be treated with the respect due to a human person. This is the foundation for the Church’s social doctrine, including its teachings on war, the use of capital punishment, euthanasia, health care, poverty and immigration. Conversely, to claim that some live human beings do not deserve respect or should not be treated as “persons” (based on changeable factors such as age, condition, location, or lack of mental or physical abilities) is to deny the very idea of inherent human rights. Such a claim undermines respect for the lives of many vulnerable people before and after birth."
The full two-page document is available at the USCCB website.