Most people are fully aware that what happened there is a tragedy. Most people also have an instant-no-thought habit to smile when having a picture taken. Is it really any better for them to take a picture and be solemn? Is that enough or do they need to express deep sadness for these pictures? Would others claim these sad emotions are just for show anyway? And if so, should we expect people to just not take pictures at all at the WTC memorial? And if so, at what point in time can we start taking pictures at a place with our normal happy faces?

People are there. They are happy they are there, even though 'there' (where ever 'there' is) may be a place that causes them to have emotions on the sad part of the emotional spectrum.

Think of funerals. It's a sad place to be (perhaps sadder since the person who died is someone well known as opposed to a lot of unknown people, but I won't judge either way). Family and friends are together, which usually makes people happy. It's a mixed bag of emotions. If someone happens to smile in a picture there it's probably more to do with habit of smiling for pictures or happiness to be with family and friends (perhaps first time in a while) than it is for being happy the deceased is deceased or for social status boosts.