I had someone suggest to me that writing “Dr. Who” is inappropriate, as it should always be “Doctor Who.”
That can only be said by someone who has only been watching for a relatively short number of years…or at least, not since the beginning.
Here is the way the credits looked back when the show first began:
And even in later times when the phrase tended not to be abbreviated in the credits, that did not mean that it was always spelled out:
And so if you think you are being a true fan by objecting to the use of “Dr. Who,” the irony is that you are in fact showing that you are a latecomer to the show and poorly informed about its history.