I'm glad Thomas Hawk raised this issue about Jill Greenberg. No matter what the cause, it is not right to manipulate children's emotions in such a way.
The general outline is that Jill is a photographer who decided that she wanted to take pictures of children crying to illustrate her opinion of the Bush administration. Rather than observe and capture natural situations in which this might occur, she created the situation by making the children cry.
From some of the comments on Thomas's post, it seems there are many people who don't seem to see what is wrong (fortunately there are plenty who do). Sometimes we look back at attitudes of only a few years ago and are amazed at what we thought was OK. I hope that this will be one of those cases.
For those that don't see the problem with manipulating children's emotions, then review the psychological experiment of J B Watson and little Albert. The poor child was conditioned to fear a toy rat. This kind of experiment is no longer ethically acceptable and is more extreme than the actions of Jill Greenberg, but it illustrates why you shouldn't mess around with children's emotions – it can stick.
Capturing the range of human emotion may be considered artistic but I think it loses all meaning when the one who is capturing it is the one who is causing it.