I think it is because the Tories and right wing press have successfully convinced a big chunk of the population that being poor is something people choose to do. They put the responsibility away from the structure of society/inherent unfairness in the system to the people who need top ups being responsible.
Eg in this mindset, people in areas destroyed by mining closures being judged as 'choosing' to be in the situation of no local jobs. People working part time so they can also care for children can just work more hours. People doing low paid jobs should have tried harder etc. And the best one of all, women who have had children should have shut their legs or not had children they cannot afford (a very common comment on the Tories fb page).
If this mindset continues, how long until people who use the NHS more than others are deemed scroungers? Why should people pay for your children's education etc. Before the NHS, people did die because they could not afford treatment.
Did David Cameron really become well off through sheer hard work? Could someone from a very poor family in a sink comprehensive really have had an equal chance to become prime minister? That's the sort of logic that Tory philosophy would have us believe. Hence the poo.
If it is truly being a scrounger to accept tax payers money, then wasn't DC a scrounger as he claimed DLA, George Osborne claimed Child Benefit, MP expenses, IDS breakfast etc. Why is it only poor people that are judged so harshly?
Tax Credits are not perfect. Our family is one earner middle but below high tax income. Yet people earning much less get about the same because they get topped up & housing benefit etc. However, I would rather this than people earning less not having enough to live on. Better to drag everyone up to a decent standard of living than drag people down.
Labour always knew that tax credits may dissuade second earners and full time work, but they thought that this was offset by having at least one in a couple working & that part time work was better than none at all.