> local SC taxpayers only get marginally more benefit than the rest of the country.

I wouldn't agree its marginally more benefit. Those bases being shut down would crush SC's economy within 50 miles of every base.

Economically, they enjoy 100% of the benefit and pay less than 5% of the costs.

The US is not, in any real sense, threatened militarily that I benefit from a large defense budget. Similar is true of food and energy subsidies. They have strategic value but they don't benefit me economically. There is a reason food and energy imports are still competitive despite the subsidies.

The benefits of what you mention is it helps broaden the US's foreign policy options, not actual economic value to the average American.