Why can't we take the law in our hands if Umar R.A. did? - Q&A - Sh. Shady Alsuleiman

Some Muslim youth believe that they can take the law in their own hands and implement the Islamic punishments etc., that are applied in Islamic states through Islamic courts. What does Islam really say about taking the law in our own hands, and can it be justified with the example of Umar R.A.?