I've always wondered, why can't we just pay one tax? Say make income tax 1.5x what it's now and cancel all other taxes. That way it'll be even easier!
Not everyone earns money via income. You have to define what "income" is exactly, then it starts getting complicated...... Example: I route my investment earning via a company, that company can claim expenses such as paying my utility bills and buying my groceries, anything leftover they give me. They work it out so my net income is zero, oops. It's easier actually to tax purchases.
Food, maybe no tax. But maybe there's some tax if it's ready-to-eat. Or based on sugar content.
Automobiles maybe taxed rather heavily, but the first $5000 is exempt so poor people can buy cheap cars, etc. It would become just as complicated as the current code.