There were two sources of opposition to the school. There have always been a small number of bigots who said the school would be a terrorist training ground or madrassa. But the much bigger group of opponents were the parents of the school where the arabic language program was to be located, namely, P.S. 282 in Park Slope, Brooklyn.
Park Slope is one of the wealthiest and whitest sections of Brooklyn, and one local elementary school is P.S. 282. But it wasn't the wealthy white families who opposed the school, because most of their kids go to private school. P.S. 282 became something of an informal magnet school for all the most ambitious, middle class, working class and poor African American, Latino and Asian families in the surrounding neighborhoods, such as Sunset Park and Crown Heights, as well as the poorer parts of Park Slope. P.S. 282 was a like black, brown, yellow bronx high school of science for baby geniuses in the middle of Park Slope.
So P.S. 282 was one of the best elementary schools in Brooklyn and one of the few routes that ambitious people of color could get a first rate public education in the borough. The parents were outraged that the Education Department was going to put middle schoolers in the already fully utilized elementary school, draining space and resources.
The parents of 282 organized, and the DOE backed down, and put the Arabic language school in a high school in Boerum Hill.
Hence the only opposition left were the nutter bigots, and the plan went forward. The press did not do a very good job of reporting what the dispute was really about.
You can get an inside view from this P.S. 282 parents blog:
http://282parents.blogspot.com/2007/03/khalil-gibran.html