I mean, For goodness sake! 9/11 was JUST as much of a tragedy to American Muslims as it was to any other American.
Maybe even MORE so because shortly after it happened their places of worship started getting vandalized and hill billys started killing, injuring, and harassing them. There are 3 proven murders that were backlash of 9/11 and more that are suspected. The FBI found a jump of hate crimes REPORTED toward muslims going from 28 in 2000 to 481 in 2001. The FBI reports say there were no slayings but multiple other reputable sources online cite at least 3 incidents of murder by people who confessed to the effect that it was a revenge killing. Just do a google search and even though it was years ago now you can still find some press articles on the vandalism that went on after 9/11
Ground Zero might be hallowed ground or whatever the fuck.. buut uh... people from a foreign country attacked us and many people turned on their fellow countrymen in truly disgusting ways. From harassment to implementing racial profiling in airports. It's been a hard time for Muslims in this country too and they have every right to worship here and to mourn what 9/11 also took from them.
I support this mosque or educational center or whatever it's going to be.. and I will pray for those who go there because I'm sure they will be harassed and abused on a regular basis for years to come by ignorant ignorant people who feel more comfortable when they can name an enemy regardless of whether the label fits.