No, bitcoin cannot kill income tax. Yes we don't have income tax to those people who are earning bitcoins. But many people are still working in a company and we're bitcoin earners are just few. So income tax is still there and if that happens each country's economy will fall down.
As of this time that bitcoin was still in developing stage then i don't think so that it will kill income taxation, but definitely it affect its revenue because more and more people is now contented to be a self employed and working in online job and as a decentralized system the government could not get tax of it. In other side i think business tax will rise also because the money that have get by the people from bitcoin will be spend to purchase goods and services then in that way the government can get tax on that business.