That pattern in the 18th and 19th centuries worked exceptionally well. New England pastors in colonial times preached and taught what the Bible says about liberty, and the Sons of Liberty—not a subset of any particular church—eventually sponsored a tea party in Boston harbor. Pastors throughout America during those centuries preached about biblical poverty-fighting, and in city after city Christians formed organizations such as (in New York) the Association for Improving the Condition of the Poor.
In the 20th and 21st centuries, government has tragically taken eminent domain over anti-poverty work. The Supreme Court has notoriously overreached by mandating abortion. The White House is now undercutting religious liberty. It's not surprising that some evangelical churches have responded with their own overreaching by becoming political and suggesting that "if only we had the right laws." But in churches that become political clubs, hubris trumps humility—and pride will go before a fall.
The scientific establishment is already falling. One recent survey showed that confidence in scientific leaders among conservatives has declined sharply over the past four decades. A large reason is the politicization of science, as many leaders demand allegiance to hypotheses about past and future—evolution and global warming—that the scientific method cannot prove.
Evangelicals need to guard against a parallel politicization of churches. Pastors as they exegete Scripture can and should make practical applications to key moral issues such as abortion, but they should be wary of going further. The Bible tells us what we need to know about past and future—how we're created and where we're going. It does not tell us precisely what to do about the Keystone pipeline or Iran's drive for nuclear weapons.
Instead of politicizing churches, we should apply C.S. Lewis' dictum: "Aim at heaven and you will get earth thrown in. Aim at earth and you get neither."