"Every competitive outcome is fair and ethical"

The Luxembourg system of taxation is competitive – there is nothing unfair or unethical about it,” Mackel said. “If companies manage to reduce their tax bills to a very low rate, that’s a problem not of one tax system but of the interaction of many tax systems.” Nicolas Mackel, chief executive of Luxembourg for Finance, a quasi-governmental agency

Putting it simple:

1 - Every competitive outcome is fair and ethical
2 - The responsibility over systemic issues (which result from the competitive actions of several agents interconnected) is a no man's land
3 - Luxembourg has no responsibility since other countries could have done exactly the same. By other words: the only reason why the Luxembourg system of taxation is competitive is because the rest of the system is dysfunctional
4 - Further competition on taxation systems would eventually result in no taxes on corporations worldwide
5 - Since that's a result of a competitive action "there is nothing unfair or unethical about it"