> The author also doesn't show how the federal income tax is fundamentally different to what an employee would pay

Not disagreeing. For anyone wondering what the fundamental differences are:

1) As an independent contractor you are responsible for 100% of your FICA tax (social security and medicare tax). For most people the tax due is 15% of your income. This is in addition to your income tax. In an employee/employer relationship the employer pays for half of this. It can be a big shock to people who are hit with this for the first time.

2) If you're an employee, your employer is automatically withholding your income tax payments for you and sending them in to the IRS at a regular interval. As an independent contractor you need to be doing this yourself. If you wait until the end of the year and pay as one lump sum you'll likely be penalized.