What is the irony Zinn tries to convey concerning John Locke?
For Zinn, the irony concerning John Locke was that his advocacy was predicated upon supporting those in the position of economic power. Zinn points out that Locke's ideas of government, popular sovereignty, and that government is responsive to the will of the people is rooted in that these people are wealthy individuals. For Zinn, this is ironic because while the American Revolution used Lockian ideas to advance the interests of "the people," it was not all the people that were kept in mind.
Zinn points out that Locke was a proponent of liberal capital wealth. Locke himself was a benefactor of the accumulation of wealth. Zinn argues this point in the idea that Locke was writing from the point of view of those who were wealthy, like he was:
Locke himself was a wealthy man, with investments in the silk trade and slave trade, income from loans and mortgages. He invested heavily in the first issue of the stock of the Bank of England, just a few years after he had written his Second Treatise as the classic statement of liberal democracy. As adviser to the Carolinas, he had suggested a government of slaveowners run by wealthy land barons.
The irony in using Locke to advance the Colonial beliefs was that Locke's theories were used, both in England and in the New World, to entrench the interests of those in the position of economic power. Locke believed that "the people" were best represented by "the middling people of England, the manufacturer, the yeoman, the merchant, the country gentleman. . . ." Locke's writings were meant to support those in the position of economic power. The Colonists appropriating these thoughts for themselves helped to further the idea that the American Revolution was "half a revolution," designed to keep the economic entrenchment constant. This becomes ironic given how the American Revolution has been depicted in the historical narrative.