I was there all morning and into the afternoon. Close up--I was with another guy on the South edge of the plaza when the second collapse happened. I wasn't aware that anyone thought ill of those who jumped but I'm not really surprised that it is possible. The situation the people in the towers were in is literally unimaginable, so we are able to imagine almost anything.
I know this because I was astonished afterwards to see how limited my own imaginative empathy is. After the first tower fell we looked for injured people on edge of the plaza but the fact that thousands were about to die in the other tower barely registered except in as much as we didn't want to get hit with any of it when it came down. (We stayed close to cover.)
We all know the famous pictures of people standing in the broken holes a hundred floors up and looking out. Obviously, I always knew in a literal sense what was going on in the pictures and in fact, people I knew were on those top floors but despite all that, for years my mind refuse to recognize the people in the pictures as terrified people seeing the end coming. It was bizarre: even though they are standing in a ruin, inches from a 1000 foot drop with smoke pouring out behind them and even though I personally fear both great heights and fire, I could only imagine them thinking about the amazing view. The view?!
It seems completely insane but it took me probably ten years before I could attach more appropriate emotions to the people in the pictures. In fact, one of my most vivid memories of that morning was an incredibly minor thing. Securities traders used to use these giant phones called turrets and there was one on the ground a block or south of the plaza that had a man's jacket all wound up in the cables. There were already tiny little yellow flags eveywhere marking people's remains, but that jacket, which must have been on the back of the man's chair, was tiny enough to grasp.