First of all, let's clarify something: I refuse to even discuss the issue if the opening line was "If he wasn't really a doctor..."
Ok? There's no "if." There's a "Now that it's been established," but that's far different from "if."
If you want to start the dialogue with "If he wasn't really a doctor," then you are starting with the premise that he WAS really a doctor, and you must thus abandon the "but it doesn't matter to me" position you took earlier, seeing as it clearly DOES matter to you.
"If the moon isn't made of green cheese, then why didn't you challenge it before you were born?"
The second half is not worth addressing because the first half is absurd.
"If Elvis isn't really alive, what about the people who've spotted him in Alabama truck stops?"
See? The second half doesn't need to be addressed because the first half is so silly.
"If Wierwille wasn't a doctor, why didn't you call him on it before he died?"
If? IF?? Ain't no if.