As someone who works in a CPA office that primarily does tax returns, and will most likely be a CPA by the end of the year, I find this suggestion truly risible. The IRS gets all the information about your income and withholding, sure, but they don’t have a clue what your deductions are. If you’re claiming the standard deduction, then your itemized deductions don’t matter, but what about exemptions? How does the IRS know if your nephew has been living with you since his parents died? Even if he’s living at the same address as you, perhaps his grandparents are providing the money and are the ones that should get the exemption. The IRS simply has no way to know about each person’s individual situation. They cannot be Big Brother.
One might say that’s a reason in favor of getting rid of most of the tax code so that what remains the IRS can figure out easily, but consider that most of the tax code isn’t there for shits and giggles - most of it is there to deal with inequities that a simpler tax code would cause to arise. Sure, some of the tax credits (Child Tax Credit, Earned Income Credit) are about addressing issues beyond simple income taxation, but by far the largest part of the tax code deals with making sure everyone is dealt with fairly.
A simple example of this that came up today (on a small scale). A couple paid property taxes and state income taxes in 2015, and deducted them on Schedule A, with total itemized deductions being around $2000 more than the standard deduction. In 2016, they received from the state a partial rebate of the property tax because of their low income that year, as well as an income tax refund. Additionally, they sold their house and some of the property taxes that they paid in 2015 were allocable to time periods in 2016, and so the buyer reimbursed them for them. All combined, they recovered around $2,500 in expenses that they had previously deducted. Thus, they had to declare these recoveries as income this year - but only in the amount that actually would have caused their taxes to go up, so only $2,000, since that was the amount of benefit that they got from itemizing their deductions.
There’s actually another step that complicates it even more, but that’s something that might be justifiably eliminated from the tax code. The above is, at least in the system we’re using, clearly what is necessary in order to be fair to both the taxpayer and the government. One way around this would be to eliminate the standard deduction entirely, and force everyone to itemize, which would mean that all recovered deductions would be income when recovered. But that would just make things more complicated for the vast majority of people who take the standard deduction right now.
All said, the IRS encourages voluntary compliance backed with semi-random audits. Taxpayers get whatever deductions, exclusions, and exemptions they determine they are eligible for, and the IRS verifies what it can automatically, and relies on the audit process to keep people mostly honest for the rest of it.
If you are among the mass of people who only have a W-2 and do not have enough expenses to itemize deductions, then the IRS could do your taxes for you. I definitely would be all for a system where you could simply tell the IRS to take your W-2 and your dependents and send you your refund (or a bill), but the IRS doesn’t get the budget to be able to support that kind of operation. The IRS is so short-budgeted that it’s estimated that for every dollar they paid in salary for auditors, they could recover at least two dollars in underpaid taxes. Obviously there are diminishing returns, but they are well short of the equilibrium point.
There are, however, Volunteer Income Tax Assistance (VITA) programs) throughout the nation that help lower-income people with their taxes. I worked a couple hundred hours for one such organization running a VITA program while going to school, and it was good experience to have on my resume even if as a CPA I will probably never deal with people with incomes of that level in my practice. It took one day of training to learn to do, perhaps another half-day for those without any knowledge of accounting at all. The IRS gives them software to use, and lets the community they are in provide the funding in order for them to provide a place of operations and the hardware (printer, computer) and paper. This is a more “American” solution of letting the free market of people’s charity dollars do the deciding of what things to support that some people feel the government should be doing themselves.