> If two consenting adults want to make a agreement that includes exchange of their own genetic information, I really don't see the issue.

The problem is one of bargaining power: Consent must be given freely – but in cases where one party in an exchange has a lot more bargaining power, the other party often will agree to something because of fear of retribution or a threat of force. Example: If an employee is told by the boss he or she will be fired if they do not have sex right now, any consent in that scenario is not given freely, but under duress.