Reading some of the comments
I can see both sides of the argument to a very great extent.
There's an often overlooked concept that permies tend to get wrong and that is that as a contractor, I don't work for the company whose site I am currently sat at, I work for a limited company that just happens to be mine. My personal employment contract, however, is with this limited company.
So in the same way if you had staff from, say, Microsoft or HP on site, you wouldn't expect those staff to be asking your manager to approve their holidays. As a courtesy, on long engagements, they would be expected to inform someone, of course.
Also, in the same way that the business-to-business contract of engagement can be terminated by either party, exactly the same is true of the business-to-business agreement between my limited company, the agency whom I work through and the end customer. You wouldn't lose any sleep at their loss but you can usually understand that they (the company they work for) are being paid because there's usually a combination of skills they cannot easily fulfill themselves and extra risk that they will be canned - as with contractors.
And yet, it's inevitable that in many cases, the people on site expect to have the right to approve or otherwise things like working hours, holiday entitlement etc etc.
Ok, so having said that, there's no way I'd ever get my company and by association myself involved in such a scheme. My own stance has always been to avoid anything that looks in any way like it's exploiting some kind of short term loophole. Ultimately, it inevitably means I pay more taxes than if I were to use them, but so be it.
And I get at least one email a day inviting me to maximise my earning so I can take home more (usually between 85 and 95% of turnover)...they go straight into my junk... indeed, I get this from "Hannah" at firstname.lastname@example.org several times a week:
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However...I don't believe the fault lies with the contractors entirely as emails like that can be tempting to some, or even the accountancy firms that cook such schemes up but mostly with the government.
Our tax laws are far too complex to be workable. Did you know, for example, that VAT is payable on adult shoes? It isn't payable on childrens shoes nor work boots. So...there is an entire section of the VAT guidelines that defines exactly what a boot is. (I will caveat that it's been a few years since I was looking at this so it _might_ have changed in the meantime).
There's also a blunderbuss approach here - rather than fight the big boys who are in cahoots with the very big accountancy firms who are, in turn, in bed with the government and get tied up in court for years, they shoot a broadside at smaller entities who cannot afford a long fight and are more likely to roll over.
I vaguely recall reading somewhere that one year, a prominent lord, paid less than £15k in taxes despite earning hundreds of millions from his various interests.
Companies do have a legal duty to minimise their costs and maximise their profit for their shareholders and that includes taxes but there needs to be a shift from both sides to make the whole thing fairer.