Hahaha
Algalon and
Skylar had explained about other's same reaction as you. Try to reread their posts to understand it better.
Also, try to reread the chapter, no, it's best for you to reread the whole Dressrosa arc and tell us which part or panel that showes Doffy's father didn't give Doffy a slave and got him in rage because of it?
There was none, was it? Since that wasn't the main reason, heck, that can not even called as a reason for Doffy to destroy the world. Hmm.......how should i simplify the logical reasons for you to understand...
Well, basically his flashback so far is as these;-
Doffy. 1-8 years old. Rich. Spoiled. Shitty brat. Suddenly. Father. Change. Live. As a commoner. Wealth gone. Mother. Died. Poor. Angry. Kill stupid father. Return. Old lifestyle. But. Other tenryuubito. Rejected. Labelled as 'traitor'. Doffy. Pissed off. Aim. World/Noble Destruction.
....Got it? :3