I understand why people get so angry about this, but realistically, if you set the rules to such a way that you make it perfectly legal to minimise your tax liability, why on earth would anyone voluntarily choose not to take advantage and pay more tax?
To illustrate my point, the tax avoidance schemes that the very rich take advantage of are all available to the rest of us. There is nothing stopping anyone from doing the same thing apart from the fact that the amount of tax you would save, would be a fraction of what it would cost to set up the structures to achieve the saving.
To put it another way; if the system was structured such that anyone could easily avoid paying tax in a legal way, do you think we would all be doing it or would we all be 'morally superior' and volunteer to pay more than we had to?
My point is that super rich people who avoid paying taxes they don't need to represents perfectly normal behaviour that any of us would also adopt given the opportunity.
The problem lies with the tax structuring itself, not with people/companies avoiding them.