Where are tax disincentives highest? cites Peter Lindert’s Growing Public: Social Spending and Economic Growth Since the Eighteenth Century to explain how welfare states might not be that inefficient:
Just as the high-budget countries often have lower marginal tax rates at the top of the income spectrum, so too they can have lower marginal tax rates at the bottom, with high marginal tax rates only across the broad middle range of incomes. If that is true, then the debate over work incentives needs to be redirected. The net effect on labor supply and GDP may depend on something never researched, namely whether work and productivity respond more sensitively to marginal tax rates in the middle range or at the ends. If the response is greater in the middle range, then the welfare state indeed reduces work and GDP. But if conservative fears are correct in emphasizing that the supply of effort is most fragile at the two ends of the income spectrum, then it is possible that the pattern of marginal tax rates in the high-budget welfare states discourages work less than the pattern prevailing in low-budget countries.