> I'd love to sign up to opt out of receiving any social security or medicaid benefits permanently for the rest of my life in exchange for a small tax credit or deduction, smaller than the amount I'd expect to receive out of these programs.

And if you go broke and end up starving on the street, everyone else just needs to bear that cost either through watching you starve to death or by paying to feed you?

It turns out that in practice, the number of people who think they can achieve your proposed outcome is far, far higher than the number that actually does achieve it.

> I'd prefer to be part of the solution to the deficit, but me leaving the country only exacerbates the problem, given that I pay in close to an order of magnitude more than I get back in return.

Sure but you're not leaving the country because, like GP, you are aware you get far more value from your taxes in indirect services.

> shouldn't I be allowed to stay and express policy preference for less defense spending

Sure can! Vote.