Mahdi Filling the Earth with Justice?

Question: What is our interpretation of stuff that people say that the Mahdi filling the earth with justice.  This hadith is Hasan(Good): 

Narrated AbuSa'id al-Khudri:

The Prophet ﷺ said: The Mahdi will be of my stock, and will have a broad forehead a prominent nose. He will fill the earth will equity and justice as it was filled with oppression and tyranny, and he will rule for seven years.

Grade: Hasan [Sunan Abi Dawood, Vol. 4, Book of Trials and Fierce Battles, Hadith 4272]

Answer: You have to read the hadith very carefully. It says: "He will fill the earth with equity and justice as it was filled with oppression and tyranny," The word "kama" mean "like" or "as", so the question ultimately arises as to how the earth was actually filled with oppression and tyranny? Did oppression and tyranny come about in an instant or even a lifetime? By no means. So, this means that, if the Mahdi would fill the earth with justice in the same ways as it was filled with injustice, it would take at least the same amount of time, if not more, as negative things, like destroying or killing do not take as much time as building and creating. Secondly, if all the prophets and messengers from Adam (as) until the Holy Prophet (saw) did not have the capacity to fill the earth with justice and peace in their lifetimes or afterwards, how then could someone, who is subordinate to the Holy Prophet (saw) do it? Why he? If God wanted to fill the earth with justice and peace, then why didn't he do it before? Why not through the Holy Prophet (saw)? Thirdly, the question arises as to how he would do it. Absolute peace and justice would mean that no human being could do anything wrong, as at the end of the day anything wrong is an injustice. This would strip human beings from their free will. Creating those people that would live at that time would have no meaning whatsoever, as they would not abstain from injustices by their own choice and thus could not be rewarded for it.