The conservative organizations Pro Sancta Ecclesia, Pro Missa Tridentina and Una Voca Deutschland say that the backlash against the pope has spiralled out of proportion. They condemn what they see as a "manipulative media campaign."
"The opponents of the pope, including unfortunately even prominent bishops within the church, will stop at nothing to stop him steering his steady course," Pro Sancta Ecclesia wrote in an advertisement in the daily Frankfurter Allgemeine.
"All the more reason for Catholics who are true to their beliefs and to the church to rise up against these attempts, stand behind the pope, and support him with prayer and work, word and deed," the group said.
The groups said that the pope can not be expected to make decisions on matters such as the lifting of excommunications based on political considerations or his popularity. The "irresponsible statements" made by Williamson do not justify such "shameless badgering" of the pontiff, the groups said.
German government's unusual move
The pope's decision to lift the excommunication of Williamson has caused particular outrage in his native Germany, where denial of the Holocaust is a crime punishable with a prison sentence.
In a highly unusual move, the row prompted Chancellor Angela Merkel to speak out, calling on the Vatican earlier this week to clarify its position. The next day, the Vatican demanded that Williamson recant his controversial views on the Holocaust, but did not reverse its decision to welcome him back into the church.
On Thursday, Merkel praised the Vatican for its response, describing it as an "important and good signal."
But it appears the row is still far from over. Many prominent Catholics say the controversy is proof that the Vatican's consultation and communication policies are flawed.
Vatican policy flawed, critics say
The head of the German Bishop's Conference, Robert Zollitsch, criticized the flow of information at the Vatican. Pope Benedict's advisors let him walk into the line of fire, Zollitsch said Thursday night in ZDF television.
On Friday, a high-level Vatican official declined to comment on the allegations of failed decision-making, saying only: "We have no FBI."
Mexican Cardinal Javier Lozano Barragan, president of the Pontifical Council for Health, was commenting on the row in an interview published by the Spanish daily El Mundo.
Barragan described Williamson's denial of the Holocaust as a "stupidity," stressing that the British-born bishop had already made the claims a year ago.
"Any one of us can say a stupidity, and are we going to be excommunicated for that?" the cardinal asked.
He explained that a stupidity was a sin if it was done "consciously and with wickedness," whereas people were excommunicated only if they "essentially disobeyed" basic dogma of the church.