All corporations organized as subsidiaries and controlled by any coal cooperative association formed in accordance with the laws of this state shall not be considered corporations organized for profit and doing business in Tennessee, or subject to any privilege tax levied by any law as a tax for the privilege of doing business for profit in Tennessee, it being the legislative intent to exempt by this section all such subsidiary corporations controlled by coal cooperative associations, where any and all profits earned by such subsidiary corporations are paid over to or expended for the benefit of such coal cooperative associations, with the result that the activities carried on by such corporations eventually promote and benefit the coal interest of this state.