> Failing/refusing to pay a subscription fee does not, generally, result in you getting thrown in a cage with rapists and murderers.

If you fail to pay the subscription fee for your gym, but break in to use the equipment anyway, it might.

To take the analogy a step further, a gym subscription is optional. Paying taxes is not.

> To take the analogy a step further, a gym subscription is optional. Paying taxes is not.

You're pushing the analogy too far. You're not an autarky, there's plenty of stuff you have to pay for that isn't optional (e.g. food, shelter, etc.).

Sometimes local mobs force you to pay them protection money. If you don't pay, they will take your property or even commit violence against you, exactly like the state. If you do pay, they will provide valuable services to you such as making sure you don't get robbed. Do you feel it would be reasonable to call this a "subscription fee"?