Read-Only Table : DISABLE VALIDATE ?

ALTER TABLE myemp MODIFY CONSTRAINT pk_myemp DISABLE VALIDATE; SQL> INSERT INTO myemp (empno) VALUES (21);

ORA-25128: No insert/update/delete on table with constraint (klabu.PK_myemp) disabled and validated

1. WHY "DISABLE VALIDATE" must disallow I/U/D on the table ?
2. Is this a "proper" way to make a table READ-ONLY ? what caveats ?

thanks

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10gR2