This graph* shows the net value to society of a person as they age. Initially, a child costs money for food, health and education. During the working years, they generate more value than they consume. In retirement, living and health costs reduce their value, but at death, there is, on average a small net value, and accumulated over many lives and millennia, these net values have accumulated to create the social assets we all share: roads, museums, libraries, scientific knowledge and technical skills.
The potential value of a person is greatest at the end of their education, and that is precisely what we are rejecting when we deport DREAMers. The benefits will all accrue to the other countries.
* The graph is an average across the population, and the exact shape will be different, e.g. there will be a steep drop at end of life. Nevertheless, the graph as drawn illustrates the point.