Do you take any deductions (i.e. the standard deduction, or itemizing)? By the reasoning of your post, that would make you "something close to evil."
I could set up my salary through some finance companies in europe that help you keep up to 85% of your salary, but I don't.
I see the danger in the system you mention that lots of money will go to niche organisations out of proportion with societies requirements. Better to pay taxes in the hope that they are distributed where they are most needed.
Speaking for myself, I enter deductions into the H&R Block program and watch the estimated payment. When the payment is something I think is reasonable, I stop entering deductions. So yes, I do send more than I have to.
(and often less, if they think they can get away with it)
Of course, it is not so easy to avoid tax as a salaried individual, which is why your comparison is failing. Somebody on PAYE (i.e. most people) can't create a clone of themselves in Ireland to pay their income tax there instead of the UK. If that option was available to individuals then I'm sure plenty would take it (assuming Irish income tax is lower, I have no idea). That is what the debate is about though: some entities have great flexibility and can avoid tax if they want, others (individuals of average means or less) don't have the choice to pay less.
On a side note, one point I've been stuck on is what to call the commentors above me. I know there's established language for it (parent, grandparent) but I have trouble using it right. Anyone know what I should have called the poster of the hypothetical, and the response that I responded to?