In many cases contractors were told that they had to register with 'umbrella schemes' like this, as it would be the only way they were paid and that it was legal.
Don't forget that contractors include quite ordinary professions - it's not all executives and senior people. There were nurses and social workers in this as well. And whilst it may have been a grey area at the time, it's worth noting that HMRC itself used this type of scheme for the contractors it hired!!
The rule has now been changed and applied retrospectively, so people who thought they were compliant have now been told that they weren't and are being given no choice about the tax demands that will start landing from April. There are people who are going to have to sell their homes or declare themselves bankrupt because they have no way of meeting the payment terms. HMRC is not allowing any kind of leeway and even MPs are starting to lobby about the fairness of this, as they have constituents who are literally going to lose everything.
I can't get that worked up about people who were mislead and as a result didn't pay enough tax. It wasn't deliberate avoidance. In terms of bolstering the coffers, why aren't HMRC going after these complex corporation structures which mean that multi-nationals like Google and Starbucks and Facebook don't pay anywhere near the level of tax that they should? HMRC reached a sweetheart deal with Vodafone that meant that the firm avoided paying £6bn in tax that it should have done!! But that's too much like hard work, and firms have deep pockets and expensive lawyers and can afford to litigate. Much easier to go after an IT contractor and who gives a shit if it means she loses her home as a result?