The former Tory leader also reiterated his support for marriage tax breaks, insisting not all relationships were equal and cohabiting parents were far more likely to split up than married ones.
The Conservatives are committed to recognising marriage in the tax system but fear Lib Dems will push it to the bottom of the Government’s agenda.
Speaking to BBC radio Mr Duncan Smith dismissed claims that the policy was sexist and outdated as a “middle class attitude”.
“What kind of a choice is it to live in a community where you are beset and you are trying to bring up kids without being able to pass on any concept of the right way to behave, that you have no man in your life who is responsible for those children, who either helps you financially or supports you.”
He went on: “This is not about choices, it’s a very middle class attitude to say it is all about choices.
“The reality is family breakdown has damaged Britain dramatically. The idea that they are all equivalent relationships is not true and the benefits system right now, it actually penalises families on lower income levels if they stay together.
“There is a real incentive under the benefits system right now to split up families. I think that is morally wrong, I think it is ridiculous.”