Who are you trying to kid?
Obviously contracts vary - and there do seem to be adverts out there for contractors to basically earn the same as perms but with zero security - those employers want their cake and eat it.
Where I work at the moment and previously, contractors doing the same role, same hours, similar work earn approx. 3x their salaried colleagues - they all know their stuff and all work hard.
They've been here longer than the permies (no job insecurity for them). Their salaries aren't included in the maths for salary bands, so they artificially deflate the average salary for the role.
They aren't doing anything illegal with tax, they aren't evading tax, but the corporation tax/income tax/making full use of tax allowances is just avoiding tax - something permies can't do. They are doing the same as Google/Amazon/IKEA et al, and of course we all know how we feel about that.
These and others are the reasons for animosity between contractors and their salaried colleagues, sometimes we hate them for it, sometimes we just take the p155. The underlying feeling is "it's not fair", which is a bit petty but it leaves me happy that Osbo is doing something about it. Although not as happy as when the loop holes are closed allowing aggressive tax avoidance by the big corporates.