Interesting diversion into the meaning of "hard" here. Like art, 'I know it when I read it.' But I think it the author has to either not violate known science (at the time of the writing) or otherwise give a cogent explanation of why and how the known science gets violated.
I agree that if you could take a particular SF story and transpose it into fantasy, historical, or other genres then it didn't pass the test. To me the "hardness" of SF is integral to the plot. My most recent favorite example author? Richard K. Morgan (Altered Carbon, Broken Angels, Woken Furies, Thirteen... haven't read Market Forces yet). Cyberpunk is a sub-genre of hard SF, right?
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