That's definitely a wrong and irresponsible answer given by CC Agent. Please report that and ask for a formal response. You are not allowed to sell it, but you can definitely book a ticket for your friend using your own miles.
This is the section you are talking about in T&C:
Alaska Airlines Mileage Plan miles, award tickets, upgrade certificates, and companion certificates may not be sold, purchased or bartered except as permitted on Points.com. Travel agents, travel arrangers and unauthorized brokers are not permitted to issue Mileage Plan tickets or to process or facilitate any other Mileage Plan transactions (including Mileage Plan account creation, account inquiries, and mileage or award ticket transfers) on behalf of others. If Alaska Airlines becomes aware that a member or a third party has misrepresented his/her identity in order to perform a Mileage Plan transaction, Alaska Airlines may, in its sole discretion, void the transaction. miles or award tickets issued, transferred or obtained in violation of these conditions of membership are voidable, in Alaska Airlines’ sole discretion. The member and/or the traveler shall be liable for the full, unrestricted value of awards issued as a result of improper or fraudulent transfers or otherwise in violation of these conditions of membership. Alaska Airlines shall not be responsible for any inconvenience, damage or loss incurred by the member or the traveler if travel is interrupted or an award ticket is invalidated due to violation of these conditions of membership. Alaska Airlines reserves the right to deactivate the Mileage Plan account and/or remove the miles from the account of any member who violates these terms until liability is fulfilled, and all other rights under applicable law to enforce these conditions of membership.
I think what it's saying is that travel arrangers can't operate on other people's account, but you definitely have every right to use your own miles. They might flag you and cancel the ticket if you just created your mileage account/don't fly with Alaska often and bought a huge chunk of miles to book the flight for your friend. However, you could totally book a flight for your friend.