In "Memory and Identity," the Pope also calls abortion a "legal extermination" comparable to attempts to wipe out Jews and other groups in the 20th century.
He also reveals that he is convinced the Turkish gunman who shot him in 1981 did not act alone and suggests that the former Communist Bloc may have been behind the plot to kill him.
The 84-year-old Pontiff's book, a highly philosophical and intricate work on the nature of good and evil, is based on conversations with philosopher friends in 1993 and later with some of his aides.
In one section about the role of lawmakers, the Pope takes another swipe at gay marriages when he refers to "pressures" on the European Parliament to allow them.
"It is legitimate and necessary to ask oneself if this is not perhaps part of a new ideology of evil, perhaps more insidious and hidden, which attempts to pit human rights against the family and against man," he writes.
The Pope's fifth book for mass circulation, issued by Italian publisher Rizzoli, sparked controversy in Germany and elsewhere after Jewish groups protested against leaked excerpts comparing the Holocaust to abortion.
In at least two sections of the book, the Pope talks about the Nazi attempt to exterminate Jews and the wholesale slaughter of political opponents by Communist regimes after World War Two.
'Legal extermination' In following paragraphs he says that legally elected parliaments in formerly totalitarian countries were today allowing what he called new forms of evil and new exterminations.
"There is still, however a legal extermination of human beings who have been conceived but not yet born," he writes.
"And this time we are talking about an extermination which has been allowed by nothing less than democratically elected parliaments where one normally hears appeals for the civil progress of society and all humanity," he writes.
In Germany, a leader of the country's Central Council of Jews called the comparison unacceptable.
At a news conference presenting the book, Cardinal Joseph Ratzinger, the Vatican's top doctrinal official, dismissed the Jewish charges.
Ratzinger said the Pope "was not trying to put the Holocaust and abortion on the same plane" but only warning that evil lurked everywhere, "even in liberal political systems."
In another section, the Pope describes at length the assassination attempt on May 13, 1981, when Turkish gunman Mehmet Ali Agca shot and nearly killed him in St Peter's Square.
Of Agca, the Pope writes the assassination attempt was "not his initiative, someone else masterminded it and someone else commissioned it."
Two trials in the early 1980s failed to prove prosecutors' suspicions that Bulgaria's secret services had masterminded a plot to kill the Pope on behalf of the Soviet Union.
At the time the Polish Pope was a strong supporter of the Solidarity trade union in his native Poland and the Soviet Union saw Solidarity as a threat to the stability of the communist bloc.
The Pope says the assassination attempt against him was perhaps "the last convulsion" of the ideologies of the 20th century -- a clear reference to the Communist bloc.