In order to speak to society to give guidance, the Church must be speak with one voice. The confusion over the issue of slavery in the Church, North and South, led to war. But in the 1850's the Church united over its opposition to abortion and so led the nation in the establishment of a national consensus against abortion, and it was made illegal (See George Grant: Third Time Around).
The present impotence of the Church in America, I assert, can be directly attributed to the quiet assimilation of eugenic, racist, and classist ideologies in the mainline denominations during the 1930's. Like Balaam's poison, the Church ingested death in the name of the "good," and so brought upon itself a legacy of corruption leading to irrelevance in social and political matters. It ceased to be the conscience of the nation when it ingested the poisonous thinking of the "quality of life" argument.
This legacy began in the 1920's with the adoption of the birth control ideologies promoted by Margaret Sanger. Any reading of her contemporary works betrays the vile racism and anti-Catholicism that motivated her. The nation, awash in immigrants from Slavic and Catholic countries, was having trouble assimilating the people. Poverty and disease were endemic among these people. It was especially evident in the New England areas. Margaret Sanger promoted her agenda, claiming that it was better for society as a whole to reduce the number of "Slavs, Hebrews, Italians" and other dysgenic peoples being born in the US. She promoted birth control as a means of reducing the reproduction of these and other undesirables, including the "colored" people. She hosted well know racists and even Hitler's eugenic mastermind in her magazine, and they contributed to her cause... mostly with the goal of preserving the influence and ascendancy of the Anglo-Saxon in the country.
That evil is bad enough, but the worse sin was that the mainline church bought into her agenda and ingested a subtle classism and racism into their moral practice. The argument of the quality of life was not spelled out, but went like this:
There are people who are less worthy, less intelligent, made a little less in the image of God than we, who need to be managed and whose breeding needs to be shepherded by our God-given superior wisdom. Since these poor creatures are not as worthy and will corrupt the purity and quality of life in the United States, we need to limit their reproduction. Of course, this is the compassionate thing to do, because these ignorant people live is squalor and poverty, and their Catholic doctrines only further their misery. We Protestants, know better, and we should stamp out such religious superstition. We are made more in the image of God and it is our God given destiny and mandate to rule...
Contemporary writings reveal how this attitude of racial superiority was a socially accepted without fear of criticism or challenge. Well known, mainline Protestant church leaders in every denomination began to support Sanger in her cause, giving her open endorsements or verbal praise. Many signed onto her manifestos. Money poured in from such wealthy scions as Ford and Rockefeller, and other bastions of American industrial wealth.
And as a result, by the 1950's virtually every protestant denomination was on board with the planned parenthood ideology (Sanger's organization became the present day Planned Parenthood), accepting it as the compassionate expression of godly wisdom for the remedy of the social ills of poverty.
However, it is the foundation of this assumption which I contend led to the contemporary impotence of the Church. Having accepted a quality of life argument, i.e., some are more in the image of God than others, the Church lost its moral authority to speak to the culture. Abortion is only the fruit of the seed ingested so long ago... if some are more worthy than others, then the killing of the unborn is obviously an act of social compassion for it prevents only the life of those who would live it miserably. It does not mar or kill the image of God, but only pieces of tissue, and is usually practiced on members of society who are inherently less valuable and less worthy.
I submit that the other errors of the Church, the questioning of the Word of God as the source of authority, the adoption of liberal humanism in the place of Orthodoxy, and the like, NONE of these errors of doctrine or practice invalidated the Church's witness. But when the Church ingested the moral poison of prejudice in the rejection of the value of all life as equally made in God's image, it lost its ability to speak coherently to the culture, it lost its unified voice, and it lost its ability to challenge the culture to moral righteousness. Like Balaam's sin, the Church corrupted itself and was henceforth open to being rejected and oppressed. The Supreme Court decisions against the Faith in the 1960's are a direct result of the Church's abandonment of the higher moral call and its consent to evil. (When salt has lost its savor, it is worthy only of being cast out and trampled on by men.) And so we live with the legacy of its irrelevance.
As evidence of this moral compromise within the Church, I would cite my experience as a former pastor in the PC (USA)... The Presbyterian Layman magazine, the conservative watch dog of the church, continually hammered the denomination over its promotion of homosexuality and radical feminism, but would not print one article against abortion. Why? Because social conservatism is not the same thing as biblical conservatism. It is okay to stand against homosexuality, because nobody likes homosexuals, but to stand against abortion is to stand against a fundamental American value of individual freedom... and the subtle classism and racism that is still present in old line conservatives. To stand against abortion created too much controversy within the conservative camp, and so it was better to avoid this issue. Even the conservative camp could not be made to speak with one voice on an issue so central to the heart of God, and with that lack of voice, the Church remains ineffective in its witness and in reversing the sins of the land. The Church cannot and does not function as the conscience of the nation on any matter: homosexuality, abortion, social programs, etc, because it has stepped down from its position of the Lord's voice. It has ceased to be salt.
Is that too highly an exalted role for the Church in society? No, for it is the plan of God that "through the Church" God would make known to the principalities and powers, the manifold wisdom of God. (Eph 3:10)
If the Church will repent, we may once again regain our rightful role - not to rule the nation as the religio-political conservatives wrongly assume is our duty - but to advise and guide the nation by speaking to its leaders the very words of God (1 Peter 4:11).