You know, with the 9/11 Mosque, people keep bringing up the nuns at Auschwitz. It was the case that the Carmelite monastery at Auschwitz was housed in the former administration buildings the SS had used during the war. They had erected wooden crosses to commemorate the deaths of Catholics at that site.
Why would they do this?
Because Auschwitz' main camp, where the monastery was housed, killed Catholics exclusively for the first 25 months of operation.
Even when Jews began to be killed at Auschwitz, they were generally not killed at the main camp, but at Birkenau, three miles away. Birkenau is considered part of the Auschwitz complex because it was a sub-camp of the original complex.
So, when international outrage forced the nuns to remove the crosses and themselves from the place of Catholic Holocaust, they were being forced out of a place dedicated to memorializing the deaths of hundreds of thousands of Catholic Poles. The commemoration of the deaths of these Catholics was essentially belittled by that removal, but the Catholic Church went along with it in order to assuage injured sensibilities.
Keep this in mind when people bring up the nuns and crosses at Auschwitz in regards to the 9/11 mosque. The comparison is actually a lot more poignant and terrible than most people realize. It would be similar to asking the memorial to fireman at 9/11 be removed because it offended the sensibilities of the families of the government employees who died there that day.
3000 people died at 9/11, all kinds of people. The strike was against American capitalism, not American firefighters or police officers. We remember the latter because of their heroism, but they weren't the primary targets.
12 million people died in the Holocaust, 6 million Jews, 3 million Catholics, but also Gypsies, Jehovah's Witnesses and many other targeted groups. The Jews were the primary targets, but the Gypsies, on a per capita basis, were probably more terribly hurt by the Holocaust than the Jews. Hitler himself said that the Catholic Church would follow the Jews into the grave, and, in some areas of Poland, he killed nearly every priest and Catholic religious. Catholicism was seen as Judaism once removed, a religion to be destroyed along with the Jewish faith.
The Muslims insistence on putting a mosque up at the Ground Zero site is very much similar to putting up a temple to National Socialism at Auschwitz. Even if most Nazis were unaware of the Holocaust, even if some Nazis opposed it when they found out about it (and many did), it's not a good idea.