You are failing to take into account that a dual-income family is twice as likely to experience a job loss.Two problems are:
1. In a single income household, someone is at home to take care of children. That person may not have marketable skills that could produce a single income stable environment.
2. 100k - 50k = 50k; 50k - 50k = 0
A two income household is more likely to have a larger cushion to take the hit, if they don't that's their own fault for living outside their means.
A single income household is at 0, less likely to have the same cushion built up to get them through the hard times.
If a single income household is bring in 100k, that may or may not be a better situation.
What if's are easy to come by in these situations, because the factors in play are variable by the people.
From what I've seen, a single income household will be hard up if the only job they have is lost.
This I think puts it best
So I'd say a two-income household SHOULD be more stable than a single-income household, but due to human nature probably isn't.