Wow..I just got caught up reading this thread, and sadly, I can't say I'm surprised. A disturbing number of kids these days seem to think that showing any sort of respect for other people, or other people's space just isn't cool.
On a travel forum about NYC, I got soundly raked over the coals by some of the posters, for wanting to pay respects in a manner appropriate to my faith, contrary to the opinions of another poster, who felt that EVERYONE who wanted to pray at the site should be redirected to St Paul's. He just didn't get that such a proposal wouldn't work for the non Christians who visit the site. Overall, I got chewed out for a host of "offenses"- wanting to pray at the site, daring to speak positively of the original WTC towers, and so on. And I wasn't the only one- other people looking to pay respects before the memorial was opened also got chewed on, their motives called into question by locals, with axes to grind about "disrespectful tourists". Some of the posters seem so nasty and hateful of tourists that I wonder why the heck they post on a travel forum at all! Really, if all they're going to do is spew the equivalent of "Get off my lawn", why bother?
So after all that ado over "prurient, rubbernecking tourists", it's a group of local students who show up, act like brats, and disgust the tourists with their antics, not the other way around.
And yes, I would be disgusted if I saw somebody throw their trash on the floor of Grand Central, or on the ground in Times Square or Central Park too. My parents taught me to respect other people and public space, shame that seems to be going out of fashion.