Understanding that birth control is renounced in Catholic doctrine, is there a sense that abortion is weightier because in involves the death of a person in addition to the ethical problems Catholics recognize in birth control in general?
Yes, there is a difference.
On the matter of abortion, the Catechism and Canon Law is explicit. It is a grave offence with instant excommunication. The penalty applies to everyone involved, including the mother if she consents and any medical personnel.
- Formal cooperation in an abortion constitutes a grave offense. The Church attaches the canonical penalty of excommunication to this crime against human life. "A person who procures a completed abortion incurs excommunication latae sententiae,"76 "by the very commission of the offense,"77 and subject to the conditions provided by Canon Law.78 The Church does not thereby intend to restrict the scope of mercy. Rather, she makes clear the gravity of the crime committed, the irreparable harm done to the innocent who is put to death, as well as to the parents and the whole of society.
However, prophylactic contraception does not attract such a penalty, although any act is intrinsically evil.
Periodic continence, that is, the methods of birth regulation based on self-observation and the use of infertile periods, is in conformity with the objective criteria of morality.157 These methods respect the bodies of the spouses, encourage tenderness between them, and favor the education of an authentic freedom. In contrast, "every action which, whether in anticipation of the conjugal act, or in its accomplishment, or in the development of its natural consequences, proposes, whether as an end or as a means, to render procreation impossible" is intrinsically evil:158
Thus the innate language that expresses the total reciprocal self-giving of husband and wife is overlaid, through contraception, by an objectively contradictory language, namely, that of not giving oneself totally to the other. This leads not only to a positive refusal to be open to life but also to a falsification of the inner truth of conjugal love, which is called upon to give itself in personal totality ... the difference, both anthropological and moral, between contraception and recourse to the rhythm of the cycle ... involves in the final analysis two irreconcilable concepts of the human person and of human sexuality.159
The Church holds that abortion is murder; it is the extinction of an existing life, with a soul. The prevention of life being created, although contrary to the natural order and the purpose of marriage and sex, is not murder.
Because abortion (including abortifacient contraception) brings a latae sententiae excommunication, the penalty can be lifted if the offender sacramentally confesses to a bishop (Canons 1355, 1357). Prophylactic contraception is an evil which can be confessed to and absolved by a priest.
76 CIC (Code of Canon Law), can. 1398.
77 CIC, can. 1314.
78 Cf. CIC, cann. 1323-1324.
157 Humane Vitae 16.
158 HV 14.
159 Familiaris Consortio 32.
To be short, abortion is murder, of a very bad type: it's so bad, that a normal priest cannot forgive anyone connected to an abortion (mother, nurses, ecc) for that sin - only a bishop is allowed to absolve that sin, and a confessor must send the sinner to the bishop as quick as possible.
Contraception, otherwise, is not necessary a sin: it depends on intention, mode, and a lot of other things - but it's never a mortal sin.