Yes, I believe that dual income is necessary in today's society. Everything cost money, the cost of living is high. If there are children involved in the household then dual income is even more necessary. Dual income may consist of two people working or one working two jobs. In the end to live comfortable, in most cases, dual income is a must.
No, a dual income is not necessary, if the family is willing to live within their means. A family can live within their means if they are willing to say no to things that they cannot afford. No matter how much or how little anyone has, they only need to live within their budget.