Both when you use it directly (which I have yet to do with a stealth bomber, unless Civ II counts) and when you indirectly benefit from a larger and healthier (thus cheaper and more productive) labor and technical pool.

As for taxes: You tax people with money; taxing people with no money tends to build deficits (not that it stopped Reagan, of course). If I can pay taxes for an Iraq invasion illegal under international law simply because a majority of our elected representatives voted for it, you can pay taxes for a perfectly constitutional healthcare bill a majority of those same representatives voted for as well.

Meh. A lot of folks would like to pick and choose what taxes they do and don't pay and each thing on which those taxes are spent. Of course, if every government expenditure without unanimous popular approval were unconstitutional I'd have gone to the SCOTUS when I was "forced" to subsidize SUVs for people who didn't need my help buying expensive, global warming, foreign oil dependent and unsafe road hogs. As the Republicans will remind us all when they have another legislative majority, if you don't like the law you change it, not get a judge to illegally annul it.