People are really understimating what the guy has really experienced in his life after they lost the CD power, they were beaten, tortured, they barely had the food to stay alive an were always on the run due to the angry mob, simply they lived like they were somewhere in middle east where its raining bombs, in this case it was raining only on them, Doffy's father was naive to think that people would be ok about an CD roaming around their island and just gulp it away like its nothing, its humans nature, everyone reeks for revenge.
Though Doflamingo had an fcked up personality from the start, I cant imagine what would the guy be like if he was a CD even today, maybe even worse than Saint charlos, and on top of it he was influenced by the cruel real world fcking up his personality even worse resulting in the current Doflamingo.
No sane and "good" person in any circumstance kills his father because his father tried something that was really good for a CD, Doffy's father is the only good person among the CD's shown until now, even though all the things also happened to Roci the guy always liked his father while in the other hand Doffy killed his father just to retain his old life and went to even kill his brother later, simply put there is nothing reasonable in Doffy's actions, he is plain evil.
