I don't think Tom Perkins was thinking of the San Francisco protests in his letter, and if he was, then he is delusional as to the current state of class relations in the US. Protests in one city over problems that are not endemic to the entire country (skyrocketing housing prices, for example) are not a rational justification for accusing the opposition of Nazi attitudes. Protests aside, inequality is a major problem in the US right now, and Perkins' response is out of touch with reality.