Except no, that’s not the case. To make the claim that all transactions that take place in the private sector are voluntary is just ludicrous and thinking typical of an an-cap that has no grasp on reality in the slightest.
The relationship between boss and worker, for instance, takes place within the private sector; and I can tell you right now that working for a fee under capitalism is not voluntary. To survive under capitalism you must work, so that you can receive money. We need money to purchase things like shelter, food and other basic necessities to live. Living in that state doesn’t sound very voluntary to me.
Roads should not be privatised. To do so would empower capitalists and give them total control over our modes of transport; something that I do not favour. It would give them authority and control over something that should belong to the community. Roads should belong to the community, not one private investor, who can decide to hike the price to whatever suits their capitalistic greed.