No association organized under this article and complying with the terms thereof 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 contract and agreements between the association and its members or any agreements authorized in this article 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.