I try to get across to my students that the government has no money of its own - everything either comes from taxes or from borrowing(which is paid off with future taxes). So in the end, most government programs involve taking money from one group and giving it to another. That's not necessarily bad (there might be a compelling reason to do so in some circumstances), but it's useful to frame things this way.
Here's a videos by Penn and Teller from their Bullsh*t (this is mostly a family friendly blog) series that hits the nail pretty much on the head:
HT: Ace of Spades, which, FWIW, is NOT a family-friendly blog. Funny, but not family friendly)