Tax avoidance is just being selfish though and causes harm to others.
I think it really should be tackled, no reason why the rich should get away with paying pretty much no tax.
The issue is that the government doesn't close up the loopholes that allow people to legally avoid tax. Take it up with them really.
I'm not rich and not even remotely close to it, so I'm not saying this to make myself feel better or anything.
People seem to have a hard time understanding that even on a flat rate percentage the rich will still be paying substantially more money than the lesser off people.
For example, 10% of £1,000,000 is significantly more than 10% of some one earning £10,000. The taxation system is hardly fair in that regard, and the government should look at the way they're spending money and sort themselves out instead of relying on money they know is coming in from an unfair system.
I don't blame anyone wanting to legally reduce their tax liability.

