A Memorial? Diane E. comes out against rebuilding the towers. She's changed her mind and wants a memorial in their place instead:

I was wrong. Don’t build offices on that space. Build a beautiful memorial park. I’m not a designer or an architect, but I have a few pointers. Make it a place of light and color, of greenery and flowers, and of peace. And most importantly--of sacred remembrance and commemoration. There's a place for commerce, and it is not there...Words cannot express, really cannot express, the feelings that I have for the kind of person who thinks that any sane human being will go to work in a building with an anti-aircraft battery on its roof.

Well, I also think the "anti-aircraft battery" stuff is ridiculous. That's a Maginot line for the 21st century. There's no way the terrorists would try a suicide hijacking again, and even if they did, why would a plane shot down over downtown Manhattan be much safer than one crashed into the World Trade Center? That said, I do think the World Trade Center should be rebuilt, with a memorial floor or something similar. And I do think that people will go back to work in those buildings, and in fairly short order. The demand for office space in downtown NY is immense, even after the WTC incident, and while the same companies may not move back in, others will take their place. I know it's a cliche, but if the WTC is not rebuilt, NY will have suffered permanent economic damage...and the terrorists will have won.