It's been a long time since I have been this divided on an issue, but the more I think about the less I become divided. While I have a strong disdain for all religions I believe in the First Amendment and people's right to believe in what they wish (with obvious public safety caveats). I personally cannot find an objective legal basis, or more accurately a rationalization, to deny the construction of the mosque. The only justification to deny the mosque is fear, intolerance and demagoguery. If I were to be completely honest I almost want to let myself base my decision on those justifications. The World Trade Center is gone. All those people are dead. For what? Religion. It disgusts me. That rationalization is easy, but it is too easy. It's why I dislike those who do base their decisions on such subjective things. It is too easy.
On the other hand, I am constantly on a vigil for so-called moderate Muslims to become a vocal force for modern, peaceful coexistence with an honest cross-cultural dialogue. I'm still looking and quite frankly I don't think it exists, at least not in any meaningful numbers. I agree with Sam Harris' contention (in the following article and in his book The End of Faith) regarding Islam as an inherently violent and intolerant religion. Possibly more so than it's Abrahamic older siblings: Christianity and Judaism.
However, even with that conclusion I disagree with Harris' central thesis that the mosque shouldn't be built. If you contend that the First Amendment to the Unites States Constitution is valid then denying the construction of the mosque is a clear violation. It would simply be giving in to our own fear, primal violence and intolerance. It's not logical. They wouldn't deny the construction of any other house of worship.
Finally, there is the fact that there are already two mosques in the vicinity of "Ground Zero" and both are over capacity. The new mosque will serve people that are regularly turned away. It will also be a multi-cultural center in the center of the most diverse city on Earth. I cannot think of a better way to advance "moderate" Islam and prove fundamentalism of any kind is insane and destructive.