Answer: The falling of the house from every side, weak and vulnerable Ushers are a clear sign that there has been a generation of careless mating.
Explanation:
In the "The fall of the house of Usher", the title means that the house of the Ushers is falling from every side. The meaning of this is that the Ushers are weak and are very vulnerable to falling sick. They have very weak immune system. All this is because of one full generation of the careless mating of the Ushers. The name of the story and the setting of the story is itself also symbolic of the spiritual, physical and mental condition of the family.
The evidence of this from the text is "with an utter desperation of soul which I can compare to no earthly sensation more properly than to the after dream of the reveler of the opium---the bitter lapse into everyday life---the hideous dropping off of the veil".
