It's only taxed if you deducted based on what you paid in the prior year. Otherwise, it's not. Example would be you deducted $1000 that you had withheld or had paid in the prior year. But when you did that year's taxes after that year's end you got $300 back. The following year that $300 would be income because you deducted $1000 but really only owed $700 that year.
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Originally, the earned income tax credit (which is more than likely why some do) was based on the theory that poorer people when they purchase things, which for them was basic living expenses, part of the costs of the things they purchased was taxes that those businesses would be paying. The earned income tax credit was to help those lower income people out by giving them a credit for those taxes that they paid. Afterall, anytime you buy something the cost of that product includes that entities taxes and all other costs associated with it. However, in todays world, this isn't necessarily the case and the amount of the credit is more politically based. The one half way good thing about it is that at least you need to earn some income in order to get it.
Here's a link that shows aquick little chart of the amounts. http://fileyourtaxesnow.com/2015-earned-income-tax-credit-eitc-chart/
