Fighting the temptation to go all "Ad hominem" ...
... hard, but must be done!
I scarcely think we would expect to find an economically "poor" fella* in the IT sector. That said, it is fair to argue that a successful contract resource is likely to have a few more pennies to toss about than a middle-of-the-road permie ... in most cases.
All this notwithstanding, I detect a sniff of your basic green-eyed monster in your comments (first para.). Please be advised that we are ALL entitled to pay the very least in tax as allowed by the law. It is not yet illegal to correctly apply tax laws so as to minimise your tax burden. Yes, it is quite true that there is greater scope for the self-employed than for the formally employed ... along with the risks, no vacation pay, no sick leave - need I go on? A moment's thought would raise many of the reasons why this has been so. You are as capable as any to work some of these out ...
Many other commentators have listed the risk factor in self-employment ... it is all very real. Very good contractors DO make a (relative) fortune .. and rightly so. So-so ones make a fair amount, and the crap ones, well, they go under sooner or later (or ... eek! ... go perm to escape the long droughts between gigs).
All I'd suggest is that until you have had the courage to go it alone, pack the green guy back in his or her box, and stop comparing apples with gherkins.
Until HMRC (or whatever tax entities apply to readers in diff'rnt locations) pull their jealous heads out of their bottoms and treat individual contractors as similarly as possible to the Capitas and their ilk out there, this will remain a silly argument between permies and contractors (and wilfully ignorant legislators).
* in fairness, on a perm salary of 60K in London, I defy anyone to not see themselves as relatively poor. In saying that, the reality for many on contracts is that they are little better off financially than the poor sod on 60K if trying to hack it in the Big Smoke.