It's not welfare but it is an entitlement. And unlike the other tax credits you listed, the EIC is a refundable tax credit, which means that you can actually get back more than you paid in federal income tax. The other taxes you mention cannot exceed the amount that you paid in. I would have no problem with the EIC if it were not completely refundable.
I don't buy into the argument that it is a refund of additional taxes paid. Social Security taxes should be "paid" back when you retire. Sales taxes are collected by the states and not the federal government. Only some excise taxes are federal in nature. Plus there is no way to quantify how much the individual tax payer actually paid in those excise taxes since many are hidden in the cost of the product being consumed.
No, they don't know how much you pay on additional taxes which is why they pro-rate it based on averages. Just like when you write off your car mileage, it's based on a pro-rated amount of the averages for gas/insurance/wear & tear.
What I've never understood is with all the tax credits out there why everyone fixates on the one tax credit that is offered for the WORKING poor. It's seems everyone is able to justify the credits they personally receive, but the working poor are an easy target because they're not "paying their fair share". Maybe if companies paid a fair wage, this wouldn't be an issue.
If I'm going to get upset about a tax credit, I'll save my anger for the credits given to big businesses to ship the jobs over seas, not on the person who's scrubbing toilets at the corporate offices.