If muslims want to buy property near ground zero and build a mosque then that is their fundamental right as free human beings. It is also their right under the 1st amendment.
If there are other people who don't like this, then the answer is to pony up more money for that same piece of land than the muslims are willing to spend to secure it. If the muslims won't sell....too bad. Crying to the government to "protect" us from the free use of private property is both stupid and wrong.
I'd heard a great deal of fussing about this business for a long time, and I'd always assumed that some government entity was involved in the building of this mosque. Now I find out that this is the work of private citizens using private property. The fair-weather conservatives who would deny them that right should be ashamed of themselves. Rights aren't just for people we like. They are for everyone.