Suppose we had a candidate who ran on a platform wherein he intended to by Executive order, legislation by his party or trying to change the constitution called for the re-institution of slavery. Would it be wrong to vote for this person even though other aspects of his agenda were acceptable? I think not.
Suppose Hitler were up for election and he promised to continue killing Jews, but he otherwise promised to be a good guy. Would it be a sin to vote for him? Yes
Understand, Obama holds the highly radical position that if the mother merely intended to abort her baby, that the baby should die. This is a truly appalling lack of respect for the sanctity of life and sets a precedent for selective euthanasia.