First there is no data I have seen that says corporations would still not move overseas.
Second lets look at some numbers. 10% tax. Person making $25,000, you take $2.5k on top of all the other taxes you still have to pay. They now have at most $22.5k to live on, to save etc. Second person is making $200,000. You take $20,000. They still have $180k. Which one of these has to choose between food, shelter clothing because of the taxes? Not the person making $200k. What good is it to the economy, to our society to have 1/10 of the low income taken by taxes? Is it fair to make someone have to choose between those things? I certainly don't believe so.
Maybe your definition of fair is your hand is your hand and if it sucks screw you we as a society don't give a crap.