For your ASL you can give such points to discuss :
*it will hamper his (friend) health.
 *eyesight or vision will be affected.
* physical exercises are necessary and he should play outdoor games inspite of watching t.v
*t.v is good source of information but there are also some vulgar things which he should avoids. 
* i dont say that tv is harmful but as u know that excess of anytging is harmful.
that's it ! hope it may be helpful to you