No insurer doing the business of sickness and accident insurance in this state shall make or permit any unfair discrimination between individuals of substantially the same hazard in the amount of premium rates charged for any policy or contract of such insurance or in the benefits payable thereunder. This section does not prohibit different premium rates, different benefits, or different underwriting procedure for individuals insured under group, franchise, or blanket plans of insurance, or for individuals insured under a policy issued to the head of a family as provided in section 3923.03.