I came across an intriguing column over at Crisis Magazine discussing whether Protestants are progressives. I think the answer is "yes," but that it requires some qualification, which is that American Protestantism is different from the European form.
European Protestantism was built around state churches that were formalized as result of the Wars of Religion. The formula Cuius Regio Eius Religio ("whose realm, his religion") placed the form of worship in the hands of secular rulers, and if the ruler was Protestant, a state church was the result.
What this did was shackle Protestants to the existing order. It was all well and good to use critical study on the Bible and deconstruct its meaning, but Nineteenth Century German theologians were still tethered to the existing political order. It was only once that order was destroyed by World War I that more radical interpretations could be given a wide hearing.
Because of the dislocation of the world wars, European Protestantism didn't swing progressive, it simply died. Yes, the remnants of state churches have embraced female clergy and now sexual liberation, but they're doing so to catch up with society, not lead it. The Marxist heresy was a much stronger influence that latter-day Lutheranism. Indeed, I'd say every European country has more practicing Marxists than state church adherents.
American Protestantism, on the other hand, cut its ties from the old regimes long ago. Only the Anglicans retained any real connection with the mother church. The other churches gradually lost that connection as the congregations assimilated into American culture. This happened for three reasons.
The first was pure logistics - it was hard to keep sending pastors across the ocean to minister to people whose knowledge of the old country rapidly faded. In time, new seminaries were established in America, but different conditions and social realities pushed them away from the home office.
Add to this the ethnic mixing that immediately took place. While inter-denominational marriage in Europe between a Swedish Lutheran and a German as possible, it was much more likely in the U.S. Many of the communities set up shop and (to give a local example) Michigan's Upper Peninsula had Finns, Swedes and Norwegians all lumped together, each with their own church. In time, intermarriage made remaining in a given liturgy less relevant.
This brings us to the nature of Protestantism to fragment and veer into new and exciting heresies. As noted above, in Europe, the requirement of obedience to the Crown kept Protestant theology in check. With that restraint removed, anyone could set up their own independent church, and many did. Those that wished to cling to legitimacy found it impossible to retain the old ethnic connections, so they created theological unions, albeit on ethnic lines.
Thus the three main Lutheran denominations in the U.S. still have an ethnic form, but it's entirely overshadowed by theology. The Missouri Synod is ethnically German, and theologically conservative. The Evangelical Lutheran Church of American (affectionately known as "Auntie ELCA"), was formed out of the Scandi churches and is very liberal. The Wisconsin Synod is also German and theologically conservative, but also extremely insular (it refuses to provide military chaplains due its distrust of government and Christian pacifism).
The same process affected other state-affiliated churches of the Reformed or Anglican nature. For example, the Methodists split from the Anglicans and have been splitting ever since.
I think this is why American Protestants fell so quickly and so thoroughly into the purely political sphere. It is also why they stopped caring about saving souls and instead busied themselves with perfecting man - and punishing the ones regarded as defective or "deplorable."
This is how we get Yard Sign Calvinists.
The Catholic Church also has its liberal/progressive wing, but it is dying off because the mainstream remains orthodox and there is an increasing focus on this orthodoxy (Pope Francis notwithstanding).
As the article states, there is a movement to try to anchor Protestantism and I agree that the effort is likely doomed to fail. Once one tries to find immutable, eternal Christian principles to hold onto , Catholicism becomes the natural choice.