What is "Dominus Iesus" and how involved was Cardinal Joseph Ratzinger, now pope, in it? Why do people care about it?

"Dominus Iesus" ("Jesus Is Lord") is the title of a document (read it) issued by the Vatican's Congregation for the Doctrine of the Faith (CDF) on Aug. 6, 2000. It was signed by Cardinal Joseph Ratzinger, who was head of the CDF during Pope John Paul II's papacy, and also by Archbishop Tarcisio Bertone, secretary of the CDF, by John Paul's explicit authority. The document thus represents the theological thinking of the new Pope Benedict XVI. The document, whose subtitle is "On the Unicity and Salvific Universality of Jesus Christ and the Church," caused immediate controversy among many Protestants because it declared that the church that Jesus Christ founded "subsists in the Catholic Church, governed by the Successor of Peter and by the bishops in communion with him." Dominus Iesus says that while Protestant churches have not been "deprived of significance and importance in the mystery of salvation," they do "suffer from defects."Many Protestants interpreted that language to mean that the Catholic Church did not regard their churches as true churches of Christ, and they argued that the language would set back the cause of ecumenicism--the reuniting of the separate branches of Christianity after the fissures of the Reformation.
The document goes on to say that the Catholic Church "rules out, in a radical way, that mentality of indifferentism 'characterized by a religious relativism which leads to the belief that 'one religion is as good as another.''"Ratzinger personally defended the document, countering that it merely restated the traditional Catholic (and Eastern Orthodox) position that Christ's church is a visible entity, in contrast to the traditional Protestant position that Christ's church is an invisible ideal in which individual communities of Christian believers participate. Nonethless, the document is still a point of tension between Catholics and Protestants.