The following is, I believe a misunderstanding on the part of the lead researcher:
Ms Marriott said despite the higher cost of tax evasion, people who committed welfare fraud were judged more harshly because society had little sympathy for people on welfare.
People have plenty of sympathy for those on welfare; for those who have suffered a redundancy, the loss of a spouse, an accident, a disability, care for disabled children etc. But fraud is an abuse of their sympathy and causes anger.
More importantly, what people have little sympathy for is the idea that the state controls all the money and it decides how much of it you can keep. Whether you personally helped create the money is immaterial.
So when an individual attempts to keep more of what he has created there is less anger than when someone tries to take what he hasn't. That is why society has greater tolerance (and exhibits it through the courts) for tax evasion than welfare fraud.