Earlier quoted context omitted.
I find the intuition that the insurers are scumbags interesting (not that I don't share it, on some level). After all, in this case they also didn't cause the problem, don't own the house, and never agreed to insure the homeowner against that kind of risk. What am I missing? Of course, its important to distinguish this situation from cases where the insurer did agree to cover it, but refuses to pay anyway.
The true villain in this story is the home inspector who was incompetent enough to miss a decommissioned upfeed hot-water heating system, a sure indicator of the presence of elemental mercury in the home.
For the most part they're just yet another guy who takes a cut whenever a house is sold.