Archbishop Joseph Naumann, Keynote Address MCC

...Catholic voters must realize that even to vote for a pro-abortion/pro-choice politician, not because of their pro-abortion position but in spite of it (because they favor other matters supported by this politician), one must have "proportionate" reasons.

Thus, they must answer the question “What could be a proportionate reason to the deaths of 40 million innocent children and 40 plus million adults scarred by their involvement in abortion?” Personally, I cannot conceive in our present circumstances what would qualify as a proportionate reason.

Keynote Address here.