I think you'll find that "paying no tax" was only really possible in the old one man band arrangements, and there are stories of people claiming daft things like driving across Europe to go out of base but the new setup has a fairly restrictive list of things you can claim, all of which are perfectly reasonable.
Most these days I would wager pay more tax than those who are employed S they are paying both sides of the NI/social insurance.
I agree if you are engaged on tax evasion on your own head be it, but that frankly just isn't the case (or even possible) for the majority these days.