Imagine a single thermonuclear explosion: one big enough to destroy a large city. The bomb doesn't weigh that much compared to the amount of energy released. A gigantic amount of energy comes from a small amount of mass. The c2 in Einstein's formula is the speed of light squared; it's a really huge number.

As for the wisdom of the NIF as public policy, that's something on which reasonable people can (and do) disagree. I'd only point out that the first government to master the goal of break-even fusion (getting more energy out of the reaction than is put in to trigger the reaction) will gain a _ridiculous_ economic advantage over the rest of the world, to say nothing of the non-economic benefits of energy independence. It's the kind of big bet that rich nations can (and in my opinion should) take.