This makes me wonder about the free rider problem. If a hostile force invades the country, what do you do with the people that are delinquent on their "Military Defense" subscription?

They wouldn't be able to live there in the first place. If you don't pay, you don't get the service.

The secret ingredient that separates a fee from tax is the same that separates sex from rape: consent.

Then there’s no difference in outcome between the options you’ve described. Nobody’s forcing you to live here, you have given consent.

That's not true. Most countries will want their share of your property of you try to move out, and some like US will try to tax you regardless of where you live.

You’re contradicting your own argument from above, and moving the goal posts. Sure the US will tax if you if you try to keep citizenship. If you wanted to do what you proposed, which is not pay for US services and not live there, then you should actually commit to moving out, right? Taxing your land on the way out is just a byproduct of living there, and happens weather or not you stay or leave. That’s a one time thing, and once you leave it’s done.

> Most countries will want their share of your property of you try to move out,

Under your model, what happens if I buy property and default on my military/police payment? Presumably I at least lose the rights to access that property, and I likely also lose rights to the property itself (since I'm no longer paying for its defense).