If you feel like our tax system is more or less unchanged and right from even before medieval times, I think few people would argue with you. During our current time of high technology, increasing automation - and cryptocurrency, the idea of a simplified and perhaps even automated tax, does sound appealing.
What could possibly go wrong? Well, I think many if not most regimes' biggest problem when it comes to taxes, beyond collections - and perhaps greatly to blame for any collections problems, is that of accountability of expenditure. Simply put, many tax payers do not understand- nor feel represented in their tax spending - even if they do agree with their political regime, which many don't.
What current accountability measures are most effective? How would a single, automated, practically invisible tax, affect accountability - and these measures? Simply put: do we currently have a practical choice, other than our votes - and our economic activity?The world is complex with many surprising feedback loops and unintended consequences - would a perfect regime for one industry or region look the same in another? For example, a single tax, say the whole tax burden was move to VAT. Authorities would still be able to prioritize certain industries over others by making those VAT exempt - but it would be harder to prioritize. Collections would go through fewer departments, giving more control to some and less to others. Discrimination on payer would be harder. On first glance it looks like a regime like this would entrench some, and marginalize others.
Contemplating this, the train of thought that there is at least some federation and distribution in my current tax-ecosystem, does help me feel better about paying my taxes, and sleep better - at least, until I can understand governance and tax better.