Why make defensive copies in getters inside immutable classes?

Question

This question is about good programming practices and avoiding potential holes.
I read Joshua Bloch\'s Effective Java and here is what I wonder:
Why should I conside

Answer 1

1 If you don't make defensive copy, you can just let your object be given out, once given out, no more your class is immutable, caller is free to change the object.

public class Immutable {
   private List<Object> something;

   public List<Object> getSomething(){
      return something; // everything goes for a toss, once caller has this, it can be changed
   }
}

2 If your field is just private and not final it means you can reinitialize the field, but if your field is final it will be initialized only once and not multiple times and you achieve immutability.