Society can always use more engineers because engineers can make jobs for themselves. In contrast, a society can not always benefit with more lawyers, for example. Not that lawyers are not important, they form an essential part of a free and democratic society. But lawyers do not produce anything, they merely reallocate money from one person to another. They make one person richer at the expense of another.
Engineering can create products and economic wealth out of nothing but mere ideas and raw materials.
In a sense, engineering can create something out of nothing. Engineers design new products our improve upon currently existing ones to drive our economic engine. Engineers currently have a tremendous impact on our lifestyles, from the introduction of more earthquake resistant buildings, faster communication networks, more efficient cars, increasingly effective missile defense systems, better imaging systems for monitoring human health, or more efficient ways of cleaning the environment. Engineering is pervasive. By choosing engineering as a profession, you are directly contributing to the well being and continued growth of society.