Attack missiles generally need to travel much farther which increases the cost. How it balances out it an open question and different for each system of missile/interceptor.
If your interceptors are good eventually the enemy is going to give up on that attack mode. - you have more incentive to defend than they do to conduct useless attacks.
If your interceptors are good eventually the enemy is going to give up on that attack mode. - you have more incentive to defend than they do to conduct useless attacks.