Wars were fought over it, philosophers argued about it then and still do now. Taxation is something that's always been and still is controversial.
The income tax has been one of the most controversial. Many don't realize that the country actually didn't even have an income tax until 1913 through a constitutional amendment, well into the industrial revolution. This was at a time where the role of government was even more unsettled than it is now.
The government was entering into areas of people's lives that would have been unthinkable by much of the population 10 or 20 years before. The urbanization of America led to things such as the regulation of food, traffic laws, housing and labor protections. All of these new ventures increased the demand for revenue, as did the concern among many in society to reduce the inequality that came about from the South's defeat in the civil war and new industries that earned vast fortunes for early tycoons in the oil, gas and railroad industry.
In addition, wealth was being created in very different ways than when America was an agricultural society. In the 1700's, most income came from owning land and selling produce or renting it out. It was easy for the the government to know how much income an acre of land would generate and tax it accordingly. With the industrial revolution, the relationship between labor and capital was different. In a minimal amount of space, fantastic wealth could be generated from a factory setting. Much of this wealth was going un-taxed.
It was in this environment of Teddy Roosevelt's term that the income tax started to be agitated for and was towards the end of Taft's term in 1913 that it was passed. Up until this time, it would have been nearly unthinkable to tax the income that someone earned. Land was taxed, there was a sales tax and a whole host of other random taxes, but income was not something people were used to having taxed.
There are still people to this day that insist the income tax is unconstitutional. Wesley Snipes, the demolition man himself went to jail for tax evasion because he doesn't accept that the government has the right to tax his income.