Tübingen became the intellectual Mecca of the radicals, however, mostly because Ernst Bloch was there. Widely seen as the father of the 1968 student movement, Bloch's Marxist analysis of Christianity and social change provided much of the intellectual architecture for the radicals, and he personally offered support for their protests. At one point, radicals spray-painted "Ernst Bloch University" over the Tübingen sign on the campus's old assembly hall. In Milestones, Ratzinger testily acknowledges Bloch's influence, saying in passing that Bloch "made Heidegger contemptible for being petty bourgeois."

Bloch was echoed by Moltmann, who developed the idea of Christian support for social revolution in his "theology of hope" (Moltmann's language reflects the influence of Bloch's masterwork, Principle of Hope). The Tübingen New Testament exegete Ernst Käsemann likewise lent his support to students who charged that the church had too often participated in the capitalist exploitation of the poor; and traditional theology frequently served the purpose of propping up the system. Käsemann, though no radical, had a keen sense of political responsibility; his daughter Elisabeth had been murdered on account of her political activity by the military junta in Argentina.

For Ratzinger, all this was simply too much. Frustrated that the theology faculties were emerging as the ideological center of the protest movement, Ratzinger joined forces with two Protestant colleagues, Ulrich Wickert and Wolfgang Beyerhaus, to "bear witness to our common faith in the living God and in Christ, the incarnate word," which the three men believed was under threat. Ratzinger found himself in conflict with many of his colleagues. "I did not want to be always forced into the contra position," he said, and thus he abandoned Tübingen, a height that most theologians can only dream of attaining, after only three years.

Ratzinger left Tübingen for a regional institution that had none of its tradition. Regensburg was a brand new creation of the Bavarian state. It was as if a senior editor at the New York Times left at the height of his career to start up a small regional newspaper in Albany. Such a decision cannot simply be explained by differing intellectual outlooks, which are, after all, the lifeblood of a great university.

It has long been rumored that one factor in Ratzinger's decision to exit Tübingen was increasing personal hostility directed at him by students. Yet he says in Milestones, "I never had difficulties with students. On the contrary, I was able to continue speaking to a lecture hall full of attentive listeners." He has specifically denied a rumor that his microphone was once snatched away from him by a hostile group of students, though the incident was reported in the German press.

Although Ratzinger did continue to be a popular teacher, he experienced strident opposition from some students and junior colleagues. It expressed itself in disturbances in Ratzinger's classes. Küng says Ratzinger, like several other popular professors, including himself, had been targeted for sit-ins by leftist students. "They came in and occupied the pulpits," Küng said. "Even for a strong personality like me this was unpleasant," Küng said. "For someone timid like Ratzinger, it was horrifying." Küng said that he cancelled his own lectures at the end of the semester in 1968 because he was tired of having them "invaded," and he said he and Ratzinger exchanged complaints about the experience. Küng said he also heard rumors during this time that Ratzinger's graduate students were unhappy with him, but he was "not very much interested in the details."

In Salt of the Earth, Ratzinger said his problems were not with students but with the "non-professorial staff." These would have been the so-called "academic middle structure," assistants to professors-equivalent to adjunct professors in the United States. On German university campuses, these were among the most aggrieved sectors, as they spent some of their most potentially productive years writing book reviews and running errands for professors. Their ordeal ended only when, and if, they too were admitted to the guild. Joined sometimes by graduate students, they often formed a second avant garde of campus unrest.

Ratzinger was also deeply disturbed by events at the student parish in Tübingen, where a group of radicals claimed the right to express a "political mandate" for the parish. These students wanted to appoint the chaplain themselves and to lead the parish into political activism. The debate deeply polarized the Catholic students at Tübingen. Ratzinger expressed his worries about the situation to his students, especially on the question of the bishop's right to appoint chaplains. It was another awakening experience for Ratzinger, an object lesson in the dangers of a politicized faith.

Ratzinger later said the Tübingen experience showed him "an instrumentalization by ideologies that were tyrannical, brutal, and cruel. That experience made it clear to me that the abuse of the faith had to be resisted precisely if one wanted to uphold the will of the council.

... I did see how real tyranny was exercised, even in brutal forms.anyone who wanted to remain a progressive in this context had to give up his integrity." According to observers who were at Tübingen in the late 1960s, several of Ratzinger's graduate students, including some who had followed him from Bonn and Münster, became puzzled and frustrated at his new stance. Some deserted him to study under Küng or Metz.