The existing tax code, along with it's subsidies, deductions, credits, etc. is a complete disaster. Tax professionals who deal with this all day, every day, for their livelihood, are unable to understand more than a fraction of the existing code, and even the people who work for the agency tasked with compliance enforcement can't begin to grasp it all in it's entirety.
As has been pointed out before, Corporations don't actually "pay" taxes, so much as they "pass the buck" on to the consumer. As such, they should not be assessed taxes, and also should not get subsidies/deductions.
Replacing the entire tax code with one paragraph. Anyone working or living in the US is required to pay 12% of all income in excess of $25,000 per year to the Treasury. Reduce IRS staff accordingly.