"f there is a private company that provides the indispensable defense, than the fee for this service is also a kind of a tax."
It surprises me that people cant grasp the difference between threats/coercion and voluntary participation. Its the same difference between rape and love making.
Service via Tax - You have no other options then to pay the tax and hopefully get what you pay for. You may or may not get the service you asked for. But it's an offer you can't refuse. If you refuse you will be put in a prison cell or killed.
Service via voluntary exchange. - You have the option to decline. You may have multiple services to choose from. If you're not satisfied with your service you can un-subscribe from their service.