Movement between companies more often than not tends to be the choice of the engineer than the choice of the company. Layoffs do occur in engineering, when markets disappear or new products replace increasingly obsolete ones, but they remain relatively rare. Our society is becoming more technologically driven, and as long as our society desires to expand on the scientific front, and as long as there is a driving force towards increased efficiency, engineers will continue to be an essential part of society. In fact, engineering is what drives an economy. It is the field that comes up with new products, better designs, and more efficient processes.
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.