Why is the tax code so convoluted that there is an entire industry devoted to following the code? It's because Congress keeps piling on the laws, exceptions, work-around, and "social engineering". Instead of adding law to the US Code, they should be removing pages from the US Code. To make things simpler, start eliminating "targeted" deductions and exemptions/exceptions to deductions, so that individuals and married people can play by the same rules as the businesses, companies, and corporations. If insurance premiums are tax-deductible to one class of taxpayer, it should be the same for all classes of taxpayers.
Completely remove the "negative tax liability". If you are going to give people money, give people money directly, and not via the IRS. The IRS is not a social agency. Their job is to collect taxes. I'm not sure what to do with tax-exempt organizations in the current climate, but the IRS shouldn't be making that determination off their own bat. They should stick to the "revenue" part.
The IRS regulations published in the Code of Federal Regulations (CFR) are to implement the statues passed by Congress. The IRS does not do this off their own bat. Court cases balloons the number of pages of interpretation, because there is no requirement to "backfill" the CFR or the USC, and stare decisis increases the amount of law surrounding tax -- another source of law bloat. That's why WestLaw and Lexus/Nexus is so necessary, and why tax attorneys demand -- and get -- such high fees. Those fees can be chickenfeed compared with the interest and penalties that their clients have to pay out when they don't use an attorney.
I don't have an opinion of the Fair Tax proposal, because I'm not sure I understand it yet. But I do know that there are way too many densely-printed pages in USC Title 26. Shrink that down to something the size of a magazine, and many of the tax ills will be solved. Ordinary people will be able to understand the law they are supposed to follow.
As a consequence, the IRS itself would shrink. And the new IT systems would be far easier and quicker to implement.
(pipe dream, for sure)