In 2014, corporations paid income tax accounting for under 10% of all taxes and 20% of all income taxes (Excluding OASDI). If you include OASDI payroll and wage taxes, corporations paid 23% of all taxes and 38% of all income+OASDI taxes.
Sales taxes, payroll taxes, and wages are paid by the consumer. These through some manner increase the cost of products directly. Income taxes skim the top: a business barely-getting-by doesn't pay income taxes. That is to say: If I pay $250,000 to employee wages, have $50,000 of other expenses, and have $310,000 of revenue, I pay income taxes on $10,000; if my operations grow 10x in size, I have $3,100,000 and pay taxes on $100,000. If I'm paying 10% on payroll, I've suddenly got to pay taxes on $250,000--and $25,000 of taxes! To compensate, I'll need more revenue; and to make more of whatever I'm supplying, I'll need more employee work time, meaning more wages, and more taxes on those wages. Basically, it means my prices have to go up by $15,000 for me to break even.
That doesn't mean a 40% business income tax is desirable. Business income taxes were $274 billion in 2013, SOMEHOW. Taxable business income was $2,090 billion, and wages were $7,633 billion. Wages would have about $1,700 billion of standard deductions, and total is $12,427 billion, so businesses would have under $1,100 billion in deductions in total.
Because it's so little, I typically ignore it as an accounting smudge. Business tax reform patently doesn't matter, and I am more interested in knocking down payroll taxes to produce the effect of lowering wages without lowering the amount of money that people actually take home. Sales taxes (and any form of VAT) also need to go away.