That's not true, and I'm not even an originalist at all. Their point is that you stick to the letter of the law (the constitution) rather than trying to bend it around current social norms and sensibilities. I've never met an originalist who thinks black people are "3/5" of a person. They will cite the 13th and 14th amendments if you do. Clearly they would feel that the Constitution shouldn't be changed ever if they felt the way you say they feel. They think if you want to change the Constitution (or laws in general) that you should pass a new law or amend the Constitution to fit the situation, not sidestep it with a liberal judge who thinks it should be interpreted through the lens of society or even social justice.