Catholic and Protestant Part Two: Sources of Doctrine

The sources of doctrine is one of the most curious issues for me right now in thinking through the Catholic and Protestant relationship. Some Protestants affirm the idea that Scripture itself is a sufficient guide for the Christian for salvation. Yet, there is a myriad of interpretations of these same Scriptures, which has resulted in a myriad of denominations. If Scripture is a sufficient guide, then why is there not more unity in the Protestant church than the Roman Catholic? If, from the Protestant view, the Catholics have obscured the gospel message with their traditions and customs, wouldn’t the fact that Protestants, who breathe the free and clear air of Scripture be able to unify in a greater degree? Do evangelicals really believe in the “no creed but Christ” mentality? If so, how is the doctrine of the Trinity to be handled? If they don’t, how should the classic idea of sola scriptura be understood?