Why is a flat rate income tax so important?

I am afraid the public discourse about the pros and cons of a flat income tax have become quite mute over time. 

However, a flat income tax should be enshrined in the constitution as a fundamental requirement! Even better, property or inheritance or wealth taxes should be abolished (e.g. because they typically amount to a form of double taxation)!

Government greed knows no bounds! The power to tax is the power to destroy!

Progressive income taxes are obviously unfair! The ability to pay is a thinly veiled pretext for expropriation by government! 

A flat income tax would force our elected lawmakers to focus government expenditures more on the truly needy. It would certainly reduce government waste, fraud, and abuse! The affluent would have less incentive to seek tax shelters or tax havens. More private, voluntary philanthropic and charitable donations would be incentivized!

Besides a flat income tax rate, the definition of income itself and any exemptions need to be carefully reviewed and monitored.