This is a good essay, but I don't think he gets it quite right. I agree with the horizontal axis: conventional vs. independent but I don't think the view he presents of aggressiveness is quite accurate.
I do think that a major axis for classifying humans is the extent to which they desire to impose their views on others through coercion. This seems to be partly what Graham is trying to capture but his description doesn't seem to quite fit. In particular I have a hard time thinking of anyone who wants to impose their own independent-mindedness on others through coercion. Typically they just want the conventional minded to leave them alone so they can work on their independent ideas and hopefully prove them right. Of course they may want to convince a few people, such as investors, of the value of their ideas before they have been proven, but that isn't the same kind of coercion that the aggressively conventional-minded employ to silence dissent.
I do think that a major axis for classifying humans is the extent to which they desire to impose their views on others through coercion. This seems to be partly what Graham is trying to capture but his description doesn't seem to quite fit. In particular I have a hard time thinking of anyone who wants to impose their own independent-mindedness on others through coercion. Typically they just want the conventional minded to leave them alone so they can work on their independent ideas and hopefully prove them right. Of course they may want to convince a few people, such as investors, of the value of their ideas before they have been proven, but that isn't the same kind of coercion that the aggressively conventional-minded employ to silence dissent.