So I probably should've made clear that I support the IRS pre-filling taxes. This would make the lives of roughly 2/3 of tax filers, the ones who take the standard deduction, much easier. That's my bad for not making this clear.
However, I think you're underselling the nuance on quite a few of your arguments.
> You realize what you're talking about (pre-filling data).. is exactly how the majority of the industrialized world do taxes.
If you're talking about "return-free" filing, sure, quite a few countries do this: http://www.taxpolicycenter.org/briefing-book/what-other-coun.... Note that these countries operate under far simpler tax systems. "Britain’s Pay As You Earn (PAYE) system, which has incorporated exact withholding since the 1940s, has several features that facilitate return-free filing. One is that it treats the individual (rather than the family) as the unit of taxation. Another is that a large proportion of taxpayers (64 percent) are taxed at the same “basic” marginal rate."
If you're referring to tax information being fully filled out, only 8 of the 35 OECD countries do so (https://www.theatlantic.com/business/archive/2016/03/the-10-...).
> You log on to a website, and if you're just taking a standard deduction, you can basically just next, next, finish your way through the whole thing, and just verify everything is correct.
See this piece from the Tax Foundation, https://taxfoundation.org/pre-filled-forms-solution-tax-comp.... The Tax Foundation has a center-right political leaning, but I think point 1 is a valid one, point 3 may or may not be. One of the advantages to using tax preparation software is that you can compare scenarios. Does it make sense to claim your college student child as a dependent? Should I itemize?
It's unclear to me what incentives the government has as the preparer of your taxes. Should they aim to collect the maximum amount of revenue? Or, should they guarantee the taxpayer the smallest possible tax burden? For grey areas, like whether your home office really qualifies as a place of business, should they pre-populate the return in a way to maximize your return?
> And of course, if your taxes are more complicated, the options for you to itemize or whatever you want are right in front of you.
You're basically suggesting that the government build online tax software with the same functionality as a TurboTax or other tax software. This is something that no government currently offers. Most OECD countries do not offer the litany of tax deductions that we have in the US. Most of these countries have no college tax credit, no mortgage interest deduction, no HSAs etc.
Some 44 million households (30.1% of the total) choose to itemize their deductions (https://taxfoundation.org/who-itemizes-deductions/). Particularly for anyone who's upper-middle class or richer, you're going to want to itemize your deductions. If you look at the sales numbers of tax software, we're looking at ~60 million copies of tax preparation software sold annually (https://www.vox.com/2016/3/29/11320386/turbotax-boycott-lobb...). So sure, there's some number of people, say ~16 million households, who should be filing a free standard deduction, but aren't for one reason or another.
The complexity of the US tax code makes what you're suggesting a complicated and difficult task. See for example, this comparison of US vs foreign tax codes (https://www.npr.org/2017/04/03/522440141/author-looks-to-oth...).
I think we agree on the basic goal of having a simpler filing option that works for the majority of people. But no other tax authority in the world has to contend with the maze of US tax law. Your own vision of an online system that lets people work through each deduction belies the fact that the US tax system is not particularly suited to the proverbial one postcard tax return.