It's all relative
You're not considering that for a Normal salaried employee their revenue IS essentially their profit!
Did they have to pay for their own office rent, their own equipment, were they 'out of pocket' while awaiting their clients/customers to actually pay them? If so, then they can claim these costs back in their tax return and receive a refund/deduction much like a sole trader.
Don't be so quick to assume that limited companies or sole traders have somehow got some amazingly better deal than salaried employees, I've been both a salaried employee and a sole trader (approx. 10 years each) and both have their pro's and con's, it is always easy to simply see the grass as being greener on the other side of the fence.
The length of time I've had to wait to be paid by clients or the dilemma of simply BEING paid by them, along with 100 other sketchy aspects I could bore you with regarding being self employed are enough to make me constantly question why I bother working for myself and don't simply go back to a guaranteed weekly wage. At the end of the day though, not being reliant on one potential asshole boss, being self sustaining and in more control of my own life/choices are the things that end up being far more important to me than a simple perceived "tax advantage" from someone who I consider 'lucky' to have a guaranteed salary.
If that still sounds like such an advantage to you then by all means feel free to become self employed yourself just get used to living with a lot less certainty and be ready to live frugally when some fucker decides they don't want to pay you 'on time' or 'at all' for work you've already done for them. If you want to take an even bigger risk then become a Limited company, risk employing some people, risk paying big money for a big office and you'll be rewarded by not being held personally financially liable when the whole thing goes 'tits up' and you walk away causing real personal financial damage to sole traders such as myself and your wage earning employees.
Like I said there are pro's and con's to all sides