You know that we just vastly simplified the tax code by changing what is and is not deductible. Most taxpayers will find the standard deduction is better for them than itemizing. Keeping track of our deductions was most of the tax complexity the vast majority of us had to deal with. There are a huge number of rules in the code to make things fair for people with special situations. It started out simple but grew over the years as new complexities arose. But for most of us, those arcane rules do not apply. For example, there is all that stuff about depreciating your oil wells. I don't know about you, but I don't have any oil wells! Most of those rules are there for a reason. You start throwing them away and some business activities become vastly profitable or economically unfeasible. You would be changing the economy for no reason other than a love of simplicity:
For every complex problem, there's a solution that is simple, neat, and wrong. H.L. Mencken
So the prudent thing is to tread carefully. Propose a change and have CBO analyze the effects before you enact it. Even something as benign sounding as charging the same tax rates on all income would be horribly disruptive. The effects would probably be a massive flight of money out of stocks, a market collapse, and a depression.
The IRS has done a great job of keeping things simple. They have a form that everybody starts with and then additional forms (with their rules) for added complexities. Most people need very few of those additional forms. I own a farm, have rentals, and usually some stocks so I need some more forms. But I find those forms pretty straightforward. They have dozens and dozens of forms I don't need to fill in. In effect, they are hiding that complexity from me because it does not apply.