Answer:
He doesn't like the fact that the society judges him by his appearance and sees him as an uneducated and violent person; however, he realizes that he can't do much to change how other people see him, especially because he grew up poor and in a lower-class family. Thus, he decides to embrace his greaser image. I think that Ponyboy was inspired by his realization that even the smartest and most well-mannered person can be seen as a greaser if he/she was poor or came from a broken family. This is why he decides to write his story not as something personal, but as something that all people who are seen as outcasts and greasers can relate to; his main reason was to provide comfort for the greasers and make them see that they are as good and as valuable as everyone else; he also wrote the story for the socs and the rest of the society, so that they can see that they are judgmental and unfair. Essentially, Ponyboy hoped to change the situation and make everyone treat each other equally and with kindness and respect.