What's the Earned Income Tax Credit if not a negative income tax?

A negative income tax is a strictly progressive income tax systems which has a range at the low end of the income scale where the marginal rate of is negative.

The EITC is not itself, and does not make the US federal income tax system, a strictly progressive system, since the EITC creates both progressive and regressive ranges.

It's not a problem. Negative income tax and EITC is another way of saying "I'm ok in theory with giving more money to the poor, but let's not divert the money from corporate profits to do that".

(that being the normal outcome of a hiked minimum wage)

It's a distraction in other words. A way to stop people demanding for a minimum wage hike.