Isn't that because in the former case it IS a crime and in the latter it is exploiting a loophole legally?It is really interesting to view the difference in the words used to describe the two actions: Welfare fraud and tax evasion. In both situations, the government (and ultimately the tax payer) is having money stolen. But only in the former case is it considered a crime. In the latter, it is accepted to be good tax payer practice.
Loopholes should be closed to stop that going on of course but while it's legal you can't really blame people for doing it if they can.