Here are the basics:
"These five current issues concern actions that are intrinsically evil and must never be promoted by the law. Intrinsically evil actions are those that fundamentally conflict with the moral law and can never be deliberately performed under any circumstances. It is a serious sin to deliberately endorse or promote any of these actions, and no candidate who really wants to advance the common good will support any action contrary to the non-negotiable principles involved in these issues.
"The Church teaches that, regarding a law permitting abortions, it is “never licit to obey it, or to take part in a propaganda campaign in favor of such a law, or to vote for it” (EV 73). Abortion is the intentional and direct killing of an innocent human being, and therefore it is a form of homicide.
"The unborn child is always an innocent party, and no law may permit the taking of his life. Even when a child is conceived through rape or incest, the fault is not the child’s, who should not suffer death for others’ sins.
"Often disguised by the name “mercy killing,” euthanasia is also a form of homicide. No person has a right to take his own life, and no one has the right to take the life of any innocent person.
"In euthanasia, the ill or elderly are killed, by action or omission, out of a misplaced sense of compassion, but true compassion cannot include intentionally doing something intrinsically evil to another person (cf. EV 73).
"3. Embryonic Stem Cell Research
"Human embryos are human beings. “Respect for the dignity of the human being excludes all experimental manipulation or exploitation of the human embryo” (CRF 4b).
"Recent scientific advances show that often medical treatments that researchers hope to develop from experimentation on embryonic stem cells can be developed by using adult stem cells instead. Adult stem cells can be obtained without doing harm to the adults from whom they come. Thus there is no valid medical argument in favor of using embryonic stem cells. And even if there were benefits to be had from such experiments, they would not justify destroying innocent embryonic humans.
"4. Human Cloning
“Attempts . . . for obtaining a human being without any connection with sexuality through ‘twin fission,’ cloning, or parthenogenesis are to be considered contrary to the moral law, since they are in opposition to the dignity both of human procreation and of the conjugal union” (RHL I:6).
"Human cloning also involves abortion because the “rejected” or “unsuccessful” embryonic clones are destroyed, yet each clone is a human being.
"5. Homosexual “Marriage”
"True marriage is the union of one man and one woman. Legal recognition of any other union as “marriage” undermines true marriage, and legal recognition of homosexual unions actually does homosexual persons a disfavor by encouraging them to persist in what is an objectively immoral arrangement.
“When legislation in favor of the recognition of homosexual unions is proposed for the first time in a legislative assembly, the Catholic lawmaker has a moral duty to express his opposition clearly and publicly and to vote against it. To vote in favor of a law so harmful to the common good is gravely immoral” (UHP 10)."
Catholics aren’t encouraged to get involved in civil disobedience. Yet, when we are faced with a situation that may involve us participating in some immoral activity, we should not participate.