We may just be having a miscommunication about scope here.
If 1/10th of 1 percent of the US population killed their family of carbon monoxide poisoning, that's 325,000 people who did it. There is no possible way that 325,000 people living today have killed their family via carbon monoxide poisoning. But even if this number was true, you are still talking about something that has happened to one person in 1000. That's already way too rare an occurrence to be the basis of an Everyman realism film
And, in fact, the total number of unintentional carbon monoxide deaths between 1999 and 2010 was about 5100 people. That would make the number of people of people who accidentally caused the problem necessarily smaller.
In comparison to the population at large, these are tiny, miniscule numbers. Not the sort of thing that virtually anyone can relate to.