Socialism could be defined on many different levels. Given that money is supposed to be a store of value, and that it has a large affect on human choices, I contend that the progressive nature of the income tax rates as they are applied at the federal level is some form of Socialism. Look at the Earned Income Credit, it pays people money back above and beyond anything they have paid in. This is a form a wealth re-distribution.

Also see how Bernie Sanders plans to use the income tax in his plan to raise max rates to 73% to accomplish wealth redistribution.

https://news.ycombinator.com/item?id=11066036