As an outsider to this discussion, to sum it up:
Germany in general thinks Erdogan is bad, he has called them Nazis + other stuff to do with his election
Ozil, who is German, meets Erdogan in London, has his picture taken with him and signs a shirt with the words "For my President"
Can refuses to meet Erdogan and Gundogan subsequently states he didn't mean the photo to be a political endorsement and he "honours German values 100%"
Germany and Ozil stink out Russia and go out in the group stage
Ozil resigns from the team saying he is discriminated against (paraphrasing)
Ozil is incredibly naive to think that his actions wouldn't piss off the German public. The word "my" on the shirt is pretty telling. He has an opportunity to clarify the situation like Gundogan did, but doesn't, implying that he did mean the photo to be a political endorsement of someone his country hates.
I'm not sure if Ozil is just completely ignorant of how he comes across and is pretty innocent or whether he does actually support Erdogan or not. Either way its best for all concerned that he retires from international football.