Society should care about the government's net inflows - outflows. If I don't pay 100 in taxes, or if I steal 100 in benefits, the net effect is the same: net inflows - outflows is reduced by 100. So they are equally bad.
I would say tax evasion (sorry Pinki), because it's usually committed by people who can afford to pay it. Benefit fraud is usually committed by people on low incomes, doing a bit of cash in hand work and the like - I'd say they need the money more so it's more forgivable.
I would say benefits fraud if the benefits you are defrauding are for such things as claiming for another house mortgage,expenses to get to the H/P when you have an apartment in London,cleaning out the moat etc.Ron.