Can you point to where the IRS has said that they can prepare returns for taxpayers?

As far as I know they can correct isolated pieces of information (e.g. wrong numbers from a W-2) but do not have the ability to prepare a return from scratch.

Edit: I mean, they can obviously put all the pieces of information they know about you onto one return and do the calculations. But there will be many pieces they don't know, and I think you are unlikely to get an accurate return without them (or based on guessing). But if the IRS says otherwise I would like to know.