The reason nearly half of Americans pay no federal taxes, this is different from other taxes (i.e., payroll, sales, etc) is that nearly half of Americans make too little money. This might come as a surprise to many given that we are the wealthiest nation on the face of the planet.
http://www.mybudget360.com/how-much-taxes-americans-pay-income-tax-us-consequence-smaller-middle-class/