The move “safeguards the IRS from an obvious conflict of interest where the tax collector becomes the tax preparer,” the bill’s summary states.
That’s a hard R in Republican
The one that affects most people is that the IRS system is "eventually consistent", but they do not currently have the information needed to file your return on the date your return is due.
If you don't believe me, request your transcript-of-records* on your account filing date. Then request it again in early fall. The latter will, IME, be complete while the former will not.
* - https://www.irs.gov/individuals/get-transcript
The one that affects only a subset of people is that many deductible items that go into tax returns are never shared with the IRS at all and only the taxpayer knows about them (today).
But we could also just make the filing deadline October for individuals. Most of those late arriving forms are K1s for partnerships that only file in April.
That said, I am solidly on board with the IRS just computing the taxes for taxpayers and sending them a bill. Taxpayers who dispute the bill can then just file their own taxes as normal.
Your personal data (age, dependents, marriage) is also in databases recording births and status changes.
For most filers, that's all you need.
I would think that they're only incentivized to accurately apply the existing tax laws, and those laws are written by a separate entity.