In the context of U.S. Constitutional interpretation, originalism is a family of theories which share the starting point that a Constitution (or statute) does not evolve in meaning, but rather, has a fixed and knowable meaning, which should be adhered to by Judges. A neologism, "originalism" is similar to legalist traditionalism, and is popular among U.S. political conservatives;
"Theory"? What would be a counter-"theory" that someone would actually stand up and go on record as advocating? I know there are plenty of non-originalist judges out there, but are there any who actually stand up and say, "I'm not an originalist"?
It'd be like saying you don't believe in the "theory" that 2+2=4.