I don't think there is a justification for big corporations to do what they do and they have to be pursued. I've been working for a bank in a tax haven in Europe and I've seen that financial engineering powerful people use has been a known and accepted tool for the governments for a while, and now that Europe is living a financial crisis governments start asking. These companies play in an absolutely different league…
Why are you blaming the companies for acting rationally, rather than the governments for creating absurd tax environments? I agree it's unfair, but I can't fault anyone for trying to legally minimize their tax burden. Tax law should just be simple enough that anyone can do it themselves.
Rational != Ethical