Economists since Adam Smith have opined that a land value tax would not cause economic inefficiency, despite their fear that other forms of taxation would do so. It would be a progressive tax, i.e. a tax paid primarily by the wealthy, that increases wages, reduces economic inequality, removes incentives to misuse real estate and reduces the vulnerability that economies face from credit and property bubbles. Early proponents of this view include radicals such as Hugo Grotius, Thomas Paine and Herbert Spencer. but the concept was widely popularized by the political economist and social reformer Henry George. Believing that people ought to own the fruits of their labor and the value of the improvements they make, George was opposed to tariffs, income taxes, sales taxes, poll taxes, property taxes (on improvements) and to any tax on production, consumption or capital wealth. George was among the staunchest defenders of free markets and his book "Protection or Free Trade" was read into the United States "Congressional Record".