We're still a heck of a lot better off than a lot of the world, after all. Why should we complain too much?
I was with you up until this part. First it makes no sense, and second it doesn't really apply at all.
First, the not making sense part. Of course we're better off than a lot of people, that doesn't mean we don't have problems. If you follow what you just said that means you should never ever complain about anything. Because, heck you're a lot better off than most of the world. It's like finding out someone's mom died and telling them so what, there are children starving to death in Africa.
It doesn't apply like at all. How is mourning on 9/11 complaining? We should just forget it ever happened and say nothing? A majority of people in America right now were alive when it happened. Of course they're going to mourn over it because it was a really big deal. Again, it's like telling someone not to be sad on the anniversary of a loved one's 'death.
I personally don't care that much about 9/11. That's mostly because I was only in 2nd grade when it happened and didn't really get how serious it was at the time. It also didn't affect me at all, I didn't lose anyone I cared about. But that doesn't mean I don't have empathy for the people that were affected by it.