I think it's not black and white. There are many people who need the support of benefits but there are also many who rely on benefits to supplement their incomes rather than earning more through work.
The thing is most of us on Mumsnet are a certain demographic: mainly women, most have children, a high proportion have young children. One of the biggest issues is the cost of childcare: what you earn as the minimum wage after tax and NI should always be more than the cost of childcare in my opinion. Other countries such as France can fund childcare properly.
It also varies massively on where you live. I have trouble with many people in London and the South East who say they can't find work. Other parts of the country are seriously short of work and it's no coincidence that they've chosen a deprived area of the NW to pilot it in (coincidentally a Labour stronghold). If they really wanted to test the model, they should pilot it somewhere like Woking.
I do agree with other posters though that this is largely ideological, wish they'd target tax evasion first.