Holy lucre ! 300 billion in lost revenue . That has to be wrong. Even at a tax rate of 30% (way higher than the US effective rate) that implies one trillion dollars each year gets hidden from the IRS. That will solve every budgetary crisis going.
And contrary to the faux Mother Theresa like notion of government that some people like to project, that money will not mostly go towards relatively positive things like feeding hungry children, giving a helping hand to out of work people, or building libraries. This extra cash will mostly go to agencies like the NSA to spy on people more, subsidies to big farming companies, payoffs to the right corrupt dictators, to the FBI to throw more people in cages for consuming a plant, or to corrupt military contractors to build more useless bombs for the next war.
The 16th Amendment (income tax) was only instituted in 1913 and the whole income tax is based on the disgraceful concept that you don't own the fruits of your labor but the government gets it before you do and only allows you whatever cut of it that they can decide on. The US was incredibly prosperous up until that time and was completely functional mostly running on limited tariffs. We would be even more prosperous today without the government sucking up such a large portion of creative wealth that exists in this country.
The IRS should flat out be abolished not just for economic reasons, but also for political reasons. It is unacceptable that they are spying on people even more and that their power can be used to target political enemies.