Well, I guess my short answer is, “So what?” Whether its 5 denominations or 20,000 denominations, the point is that unless God had provided for an established visible authority, there would be no guarantee that the objective truth of the Gospel would be preserved. All you have to do is look at the various Canonical lists of Scripture to realize that the Church had to have some kind of infallible authority to even come up with a canon of Scripture.
Just ask a protestant how he knows that the epistle of James should be in the canon of Scripture? or Revelation? or one of the Gospels? Why not throw out a book or two if it contradicts the theological perspective of my church?
History, reason, and common sense shows us that most people do not have the education and rational skills to decide these matters for themselves. That is one reason why Christ established an objective authority to be obeyed by the laity. If salvation and truth were only accessible to those who could do in depth research, then the vast majority of humanity would be excluded.