As Einstein said repeatedly, in many different ways, a solution should be as simple as possible, but not simpler. What you are proposing falls into that mistake. Tax code is complicated because economic activities are complicated. If you get rid of all that code, lots of economic activities just don't work any more. In other words, it would tear the hell out of our economy and send us into a deep depression. We would have a fundamentally different system, and lots of very good things would no longer be possible. For example, home ownership.
On the other hand, this is just the kind of thing Trump likes: Some overly simplistic solution and damn the consequences. So we may suffer something like it, God help us.
99% of those rules are there for the purpose of equity, not for special interests. Get rid of them and equity flies out the window.
