Great question...
The rule says (and I'm quoting from memory not a direct rule), "recreate the inning as if no error occured, always giving the benefit of the doubt to the pitcher in determining how many bases a runner would've advanced in determining earned runs".
So, the question would be to you; apply that logic and decide if a runner would've scored from first without any doubt on the double. I would ask myself, "was the hitter a Clidesdale (sp?) and any other hitter in the lineup would've had a triple?" If answer to that question is "no", then I score unearned.
Just me...
Bottom line, scoring a run unearned helps the pitcher and doesn't hurt the offense, which is why the rule is phrased the way it is.