"Being Faithful"

I want to pursue one point in John Breen's response to my earlier posting becuase I think it addresses a fundamentally important question. John says, "isn't it more important to be faithful than to be effective? That is, because we are dealing in the case of abortion with the foundational issue of who counts as a member of our society (i.e. who is a person) perhaps our vote should stand on the principle of the matter rather than on causal arguments open to serious challenge."
I think the question is what does it mean to be faithful in this case. That is, is an act of greater faithfulness for one who is morally opposed to abortion to vote for (i) a candidate who says he is against abortion if one believes the candidate's policies are not the most condusive to eliminating abortion or to promoting the sanctity of life from conception to death; or (ii) a candidate who says he is pro-choice but whose social welfare policies (access to health care, minimum wage, etc) one believes are more likely to create a situation where fewer people feel trapped into having an abortion and whose policies one believes are overall more promotive of sanctity of life. (I recognize that at some level this is too simplistic - there is a lot else that is required to try to eliminate abortions, and whoever is elected those things need to be done.)
As I was thinking of this the other day, what came to mind was the parable of the two sons in Matthew. A man asked his two sons to go and work in the vineyard. One told the father no, but afterward changed his mind and went. The other said yes, but did not go. The answer to Jesus question of which did the will of the father was the first, not the second. (Jesus went on to tell his followers that tax collectors and prostittues are entering the kingdom of God before them.)
I struggle with this issue and would be happy to hear from others (assuminmg there are people not yet tired of this thread).
--Susan