> 10% flat federal sales tax

Rich folks only need so many mansions, yachts and designer sweat pants. This would further shift the burden of taxes onto lower income folks who spend 100% of what they earn.

The IRS could just present a form behind a login with an itemized fully calculated tax return with an accept? "yes" / "no". They already have all the information they need, and already do the work when checking returns for errors.

Taxes are a pain because both, corporate capture of government by powerful tax preparation companies and also because a certain political ideology wants paying taxes to be as unpleasant as possible to make the concept of taxes as unpopular as possible.