David and Collin, I think the connection between Calvinism and the Baptist heritage is more than just about historical overlap. The question of just how much those two categories really overlap in history is very hotly contested, but that’s not the only reason to bring other dimensions into the discussion.
To the question, “why Calvinist Baptists rather than Lutheran Baptists?” we might add the question “why Arminian Baptists rather than Lutheran Baptists?” You’re right that there is a lot of important overlap between Calvin’s soteriology and Luther’s—although the differences, such as how we account for the lost relative to God’s decree, are worth noting. But the Lutheran tradition did not maintain the robust Augustinianism of its founder; under the influence of Melanchthon and others it quickly became mostly what we now call Arminian. So why do we now speak of that view as the Arminian view rather than the Lutheran view, when in fact Melanchthon and other Lutherans reached it first? You could of course reply once again by tracing historical events, and that would be valid but I think there is more to the story.
I think there are specific things about the Calvinist version of Augustinian soteriology that made it more likely, and still make it more likely, than Lutheran or Anglican versions to find acceptance in Baptist or Free Church traditions. And I think this also explains why Baptists who are not Calvinists are Arminians—what distinguishes Arminianism from the Lutheran or Anglican versions of that soteriology is that it arose among a confessionally Calvinist church, as a specific response to Calvinism, and thus shares some of the methodological qualities of Calvinism even though it disagrees theologically.
(As a side note, but one with a lot of relevance here, the question “What is Calvinism?” is an old one and there has never been any consensus about it. Enough people use “Calvinism” to refer solely to the soteriology that has developed in the theological school that traces its roots through Calvin (and others, such as Augustine and Luther) that you can’t really call it wrong to use the term that way. But enough people use “Calvinism” to refer to the coherent whole of Reformed theology as it developed after Calvin (such as one finds in the Westminster standards) that you can’t really call that use wrong, either. And enough people use it to refer to the thought of John Calvin the individual, without reference to theological traditions either before or after, that this use is also in bounds.
Although people were debating the question “what is Calvinism?” well back into the nineteenth century, the tendency to identify Calvinism exclusively with a soteriology became dominant only in the twentieth century. Ken Stewart has done yeoman’s work digging up the history on this, and I highly recommend the overview in his Ten Myths About Calvinism, from which I borrowed shamelessly in my own book on the subject.)
For transparency I should state that I currently have a foot in both worlds. I am by conviction a Presbyterian and spent the first decade of my Christian life worshipping in confessional Presbyterian churches, and would prefer to continue that practice if I could. However, due to my location and family circumstances I am not currently able to do so, and we are now very happily worshipping as “associate members” of a Baptist church—”associate” because we will not be baptized as adults. So I hope I can do some justice to both sides when considering why the soteriology first developed by my Presbyterian forebears might be more likely to be appropriated by my Baptist brothers.
1) Calvinist (and consequently Arminian) theology is clearer. Our Lutheran brothers say that asking the big questions leads only to paradoxes, of which the lowly human mind cannot say much that is meaningful. Meanwhile, our Anglican brothers may have clear personal opinions about the answers to these questions, but when setting direction for the church at large they drape a graceful veil of ambiguity over them for the sake of unity. The confessional Calvinist finds this insufficient—not because he has a high opinion of human reason, but because he believes God has told us clearly and consistently what we are to believe regarding these questions, and the pastor must preach the whole counsel of God. Rising in response, the confessional Arminian agrees that God has told us what to believe, disagreeing only on what God has said. It seems to me that Baptist and Free Church communities generally require this level of clarity in their theology; a large-scale commitment to paradoxes and ambiguity in theology is only sustainable in the context of a broader coherence of tradition and culture that magisterial churches presuppose but Baptist churches do not. (In reference to David’s post I would note that ecclesiology is not the issue here; churches in the magisterial traditions can practice congregational polity while presupposing a shared intellectual/cultural life embodied in church tradition, which Baptist and Free Church communities do not wish to presuppose.)
2) Calvinist (and consequently Arminian) theology is more culturally prophetic. The Lutheran insistence on humble paradox and the Anglican insistence on graceful ambiguity prevent both traditions from being proactive and systematic in challenging the structures of human culture. H. Richard Niebuhr got a lot of the details wrong, but he was basically right that the theology of paradox creates a sort of amphibious creature who can be inwardly transformed by the Spirit in a radical way, but outwardly has a tendency to conform to the structures of his culture as given. Meanwhile, the ambiguity of Anglican theology means Erastianism and accommodation to the dominant culture is more or less a given for Anglicans. The Calvinist, and with him the Arminian, again finds this insufficient. Just as we are clear about our theology, we are clear about its cultural consequences. Baptist and Free Church communities define themselves in opposition to the magisterial traditions because of what they see as the magisterials’ captivity to the dominant culture, so the ability to support a robust prophetic voice is indispensable to their theology.
3) Calvinist (and consequently Arminian) theology is more culturally adaptable. This may seem counter-intuitive given the claim that Calvinism and Arminianism are more prophetic, but I believe it is not. Calvinism/Arminianism are more likely to become prophetic wherever they are planted, but they are also more easy to transfer from one soil to another. This goes back to point number one; Lutheran and Anglican traditions are harder to spread to new cultures because their commitment to paradox and ambiguity presupposes a coherent intellectual and cultural tradition. While the magisterial Calvinist traditions such as Presbyterianism also presuppose the coherence of tradition, their greater clarity about what they are claiming and why makes the cross-cultural encounter much easier. This is why it was Calvin’s Geneva, not Wittenberg or London, that planted Protestantism across half the globe in the first century after the Reformation. The value of this clarity for facilitating cross-cultural encounters is also at work among Baptist and Free Church communities, which makes Calvinism and Arminianism easier to accept there.
Of course, the tension between understanding “Calvinism” as a soteriology or as a larger theological tradition remains. David’s post reflects an expectation (typical of the magisterial approach to which he adheres) that he who accepts the soteriology must then at least wrestle with the broader tradition, because the tradition is coherent. Collin’s post, reflecting the Baptist outlook, presupposes no such coherence; he is not explicitly hostile to the idea, but he clearly does not take it as a methodological starting point. I am, as I have said, on David’s side of that question. But my experience worshipping in a Baptist church leads me to see Collin’s viewpoint more “from the inside” than I used to.