Re: A useful little test
You seem to be talking about the USA, but things might be a bit different in the UK, as I now explain. In the UK, "tax evasion" refers to an ILLEGAL way to not pay tax, and "tax avoidance" is a LEGAL way to not pay tax. So, the statements "tax avoidance is completely legal" is correct, as is the statement "tax evasion is illegal".
In an effort to encourage people to save/invest, the UK government has "ISA" (individual savings accounts) which is a tax avoidance wrapper around saving/investing accounts. You can put in up to £20,000 per year into an ISA. Whatever gains you get in an ISA are completely tax free.
Clearly, ISA is a (legal) tax avoidance scheme that is ENCOURAGED by the government (rather than being a loophole they have failed to close). I have several books on my shelves on topics such as "how to reduce taxes for a small business" and "how to pass on your wealth to your kids to reduce inheritance tax". Such books provide numerous examples of (legal and even encouraged) tax avoidance.
Contributions into a pension fund are free-of-income tax, and when you reach retirement age you can take out 25% of the fund tax free (again, legal and encouraged tax avoidance), and then take out the remainder at your then tax rate. Since a person is likely to have a lower income during retirement than during their working years, the "deferred tax payment" of a pension is also a form of (partial and encouraged) tax avoidance.
I haven't bothered to read the entire thread you and Anonymous Coward are participating in, but I figured I should explain the above in case differences in laws in different countries might be partially fuelling the anger.
Some tax avoidance techniques are of the "uninended loopholes that haven't been closed yet" variety, but some other tax avoidance techniques are of the "the government ENCOURAGES you to use this to reduce taxes" variety.