Which brings us to the second question; is the view of the church as "exclusive" through history accurate? There seems to be 2 views that permeate the radically inclusive camp. The first is that the Church was very inclusive during the New Testament period and perhaps for a few centuries afterwards, and the second is that things actually got screwed up pretty early on with the coming of that homophobic misogynist Paul. From a cursory review of history and a certain point of view, the first actually has a ring of truth to it, while the second - from any standpoint - is laughably ridiculous. If you take Paul at his word, and I see no reason why anyone should not, he was specifically chosen by God to be a missionary and, though it is not explicitly stated, to write much of the New Testament. For Paul's theology and ecclesiology to be a mistake, one would have to accuse God of stupidity, ignorance or downright ill-temperedness to foist such a problematic authority on the church.
So let's examine the first - the church started out following Jesus' example and did so successfully for a few hundred years, but over time a bunch of man-made traditions, mostly sponsored by power-hungry male bishops and church leaders, were heaved upon the church and a spirit of exclusionary zeal came to prominence. As I said, from a certain point of view and a skimming of history, this sounds true. By the end of the 2nd century, the church was starting to express its belief in apologetical materials, which served as exclusionary vehicles in some ways. Saying "THIS is what we believe" necessarily implies that if you believe "THAT", you are not one of us. The church was also facing some of the initial gnostic heresies, which resulted in a great deal of exclusion if you are among the Pagels' camp that thinks the gnostics had as much of a claim to orthodoxy as the Christians did. Of course, this tendency to define the limits of right-belief only became more pronounced in the face of greater and more insiduous heresies like Arianism, which came later. Was the church "exclusive"? Yes, it was. But....
But this can only be understood in the negative sense if you have a flawed understanding of Jesus and misunderstand that nature of theology. First, theology is not merely "stuff we say about God," which is a definition I have heard several times from the pomo-emergent arena. That definition moves theology from being God-centered, to being self-centered, and allows us to define God by our own predilections and tastes. A necessary move if you want to be radically inclusive, since we have already seen that Jesus was not. But, if theology is kept God-centered, then theology becomes objectively true and it is more than a mere descriptor of God-in-our-image; it describes God-as-who-he-is. Admittedly, such a definition of theology is all but impossible in Protestantism since there are so many variations. While a Calvinist or a Lutheran may truly believe that their theology is correct, their theology also requires that they acknowledge the Christianism (to coin a sour phrase) of other different-believing Christians. Such acknowledgement subtlely undermines a God-centered theology, since you are in effect admitting that the other point of view may actually be correct, thus leading to relativism. Second, God-centered theology that is objectively true and is an accurate description of God requires us to believe that right-belief is actually very important, since anything other than right-belief must be wrong! Truth becomes of paramount importance and necessitates that the church mobilize itself in defense of it. The exclusionary zeal of the church - in its apologetics, in the persecution of heresy and the definition of right-belief - is a good thing in the context of a proper understanding of theology, since anything less is compromise. In certain circumstances, one could easily argue that the church, rather than being too exclusive, was not exclusive enough!