Usually when rich people rage against the possibility that someone less wealthy might become their neighbor, nobody bats an eye. Why would they? NIMBYism is the dominant fact of American urban geography. But in recent years, a number of very rich people, including the billionaire investor Marc Andreessen, have positioned themselves on the other side of the debate, arguing against supply restrictions and deriding purportedly progressive places for failing to address the rising cost of housing.Andreessen is not just your run-of-the-mill billionaire; he’s the co-founder of the venture-capital firm Andreessen Horowitz and a Silicon Valley bigwig.