From the Anti-Defamation League's own timeline:
ADL learned two very significant lessons in the 1920's: achieving equality needed affirmative techniques as well as defensive efforts, and the welfare of any one minority was intertwined with the welfare of all.
ADL head Abraham Foxman, 2010:
The issue was wrenching for the Anti-Defamation League, which in the past has spoken out against anti-Islamic sentiment. But its national director, Abraham H. Foxman, said in an interview on Friday that the organization came to the conclusion that the location was offensive to families of victims of Sept. 11, and he suggested that the center’s backers should look for a site “a mile away.”
“It’s the wrong place,” Mr. Foxman said. “Find another place.”
Asked why the opposition of the families was so pivotal in the decision, Mr. Foxman, a Holocaust survivor, said they were entitled to their emotions.
“Survivors of the Holocaust are entitled to feelings that are irrational,” he said. Referring to the loved ones of Sept. 11 victims, he said, “Their anguish entitles them to positions that others would categorize as irrational or bigoted.”
Of course families of 9/11 victims are entitled to "feelings that are irrational or bigoted." Last time I checked, the Constitution guarantees everyone their entitlement to those kinds of feelings regardless of whether or not they've lost a loved one to terrorist violence. What it doesn't guarantee is the right to tell people where they can build based on the fact that they happen to be of a particular faith. What's tragic is that the ADL of 1920 would have understood the difference.