No association organized hereunder and complying with the terms hereof shall be deemed to be a conspiracy or a combination in restraint of trade or an illegal monopoly; or an attempt to lessen competition or to fix prices arbitrarily nor shall the marketing contracts and agreements between the association and its members or any agreements authorized in this chapter, be considered illegal as such or in unlawful restraint of trade or as part of a conspiracy or combination to accomplish an improper or illegal purpose.