David Aaronovitch asked a good question in the Times this morning. It's behind a paywall so I won't quote exactly but the essence was simply "what would happen if everyone did a Jimmy Carr and did not pay their tax"?
No social services (and wait until you or a relative need them - and then see what you think)
No law and order.
And on and on.
Society would fail.
That's what happen when people free-ride.
That's why tax avoidance is immoral. Free-riding is cheating the rest of society. At cost to us all.