So what's the best and most appropriate thing to do?
Run
to 9-11. Embrace it.
There isn't a doubt in my mind this mosque should be built. Not one. But I know good people whom oppose -- for reasons I've stated on numerous occasions -- and I respect their view, even in disagreement. The potential gains for the extremist/"bad" Muslims and the resentment they have for "good" Muslims allowing that potential outcome is just too much to bear -- 9-11 brings forth just too much emotional baggage and an unwillingness to allow any kind of dishonor to come to those victim's memory; and not from the vast majority of Muslims but from those that would use the new mosque's building and location as validation to their cause.
Like it or not, America and the real world isn't a utopia. There's a give and take we all have deal with to make things work, even sometimes when we're in the right -- baggage, perceptions, ignorance, etc., exist in us all and are brought to the table when dealing with anything, whether it's a people or view. America wasn't founded on Islamic principles. Islam may be the largest faith there is, but it ain't in America. Islam is a minority and, thus, is not as well know or understood. Therefore, it's going to take a little extra effot on their behalf to assimilate and find common ground and understanding with their fellow Americans. It's no different than if you're a foreign-exchange student, really. Perceptions, misconceptions, ignorance and the ability to get passed them, take time and an effort on your behalf. If you want to make friends and find acceptance, you have to be willing to put yourself out there -- sitting by yourself or with the two or three people like you isn't going to help your cause.
Back to 9-11 and running to it. How do you make this thing a positive for the Muslim-American community and take away any kind of promotion/fuel for the extremist's cause?
Simple. Use some common sense.
Dedicate the community center to the memory of those that lost their lives on 9-11. Put some kind of commemorative plaque or statue outside the community center as a sign of solidarity to your fellow Americans. Show that the actions were not only an affront to America and its ideals, but to Islam and what it truly means to be a Muslim -- convert the convertible with actions of good faith.
There will always be cooks. Always. But if the people responsible for this community center just make a small gesture like that, they take away any kind of unease from those with genuine objection. They'll also allow themselves the opportunity to win over and convert the legitimately ignorant.
But that's just too commonsensical and stuff.