Who won the great debate in the 1920s about the future: the modernists or the fundamentalists?
At the time, the modernists won the debate. However, the debate is in some ways still being waged and the fundamentalists have retaken some of the ground in the US today.
In general, society has become much more "modern." To take one very obvious example, women have much more freedom and a greater place in society today. Religious orthodoxy has much less control of society today, with many fewer places having "blue laws" (restriction to activity on Sunday) and with the disappearance of things like organized teaching of religious values in public school. In these ways, the modernists have won. Society will never be as traditional or as dominated by religion as it was in those times.
However, on some issues, the debate is not at all over. Fundamentalists can be said to have won the debate over evolution, for example. If polls are to be believed, a large percentage of Americans do not believe in evolution and there are places where alternative explanations must be taught by law in addition to evolution. In this way, at least, the debate is not over.