Some people just don't care.

 Sometimes people forget that they are not the center of the universe and don't look at the whole scheme of things and this can have terrible side effects. That is why we have the Hippocratic Oath, " First, Do no harm." But some people don't really care about the rest of the world. In the twenties, people weren't really concerned about the future. They speculated and bought everything on credit to fulfill their need for instant gratification but didn't care about the economy as a whole. They played with the economy like it was a jenga tower but didn't care that the blocks were falling down. Similarly, Daisy and Tom threw Gatsby under the bus when they blamed him for Myrtle's Death. Tom already knew that Wilson had lost it but didn't care who Wilson hurt as long as it wasn't him. Daisy and Tom represent the careless attitude of the twenties. Fitzgerald states that they "smashed up things and creatures and then retreated back. "

In Econ. , a few weeks ago, we discussed the Tragedy of the Commons where the public sheep grazing area was overgrazed as people didn't care about the land. However, when the govt sold individual plots of land, people took care of it. The whole concept of externalities is based on the fact that people can have an impact on things that they don't have anything to do with. In the more global world this has to be taken into account and people should try to help have a positive impact instead of ignoring the world.
in the dark knight, Alfred has a really awesome line when he tells Batman "Some people just want to watch the world burn." I believe he is commenting on how some people just don't care what happens to the world as long as their needs are met and may actually take pleasure in the destruction. That is definitely the case with Tom and Daisy as in their mind, the world is their oyster and theirs alone to use up in any way they would like.