Not everyone is salaried, especially at these levels where you're not earning enough to pay any income tax.

Hourly employees pay it too and because it is a withholding tax, you pay for it even if you are below the standard deduction and don't file a tax return because it is automatically taken out of your paycheck by your employer when you get paid. Self employed people also have to pay both sides of it and they have to file if their income is above $400 a year so the only way your really getting out of it is if your employer is paying you under the table or you are self employed and made less than $400.