So on that note, Nathan Finn has written a short series of posts at the consistently thoughtful Between the Times blog that examines the question (parts 1 2 3). Here are his conclusions (from parts 2 and 3):
I am in favor of breaking out of the too-simplistic either/or approaches to Baptist origins (Anabaptists versus English Separatists, apostolic origins versus post-Reformation origins). The portrait is too complicated for tidy answers.and
The English Baptists represent the culmination of the reformation era, agreeing with the basic evangelical soteriology of the magisterial reformers and some Anabaptists and the radical ecclesiology of the orthodox Anabaptists and some English Separatists. They also recognized and appreciated that some medieval sects were correct in at least some aspects of their ecclesiology. But Baptists did not agree with these positions because they were affirmed by Waldenses, Lutherans, Reformed, or Anabaptists, but because Baptists believed an evangelical gospel and a free believers’ church represented the heart of New Testament Christianity.
The question of Baptist origins is best answered with a both/and rather than an either/or. The 400th anniversary of the Baptist movement seems like a great time to rethink our origins and appreciate the polygenetic theological roots of the Christian people called Baptists.
To summarize, I do not believe there is any historical reason to ignore Anabaptist influence upon the Baptists, though I also do not wish to see an overemphasis on this point. As I mentioned in my previous article, I suspect there are several reasons for contemporary hesitancy in this matter. Some Baptists shudder at Anabaptist sectarianism. So do I. Some Calvinistic Baptists are uncomfortable with the Anabaptist emphasis on libertarian free will, sometimes de-emphasis of justification by faith, and fuzziness on substitutionary atonement. Ditto. Lots of Baptists are skittish about the lunatic fringe of Anabaptism. You betcha. And some seem to suspect there are present attempts to “Anabaptize” the SBC. And there may be. But none of this changes what I think is good historical evidence that the earliest Baptists were influenced, to varying degrees, by some Anabaptists.That was actually my working hypothesis as I head into some reading on the issue (as soon as I'm done with this book), but Finn's no doubt read a hundred times as much on the topic as I have, so take his word, not mine. Since Finn cites the two books I'm planning to read, Verduin and Estep, I'm guessing my opinion won't move much.