It's an -ism, definitely; it's recognisably the same set of thought pattersn as racism, but directed against the past. Ancestorism?

It definitely is an -ism! It drives me crazy how people also assume that ancient peoples-- and not even like Neolithics, but people who only lived 2000 years ago or something-- were stupid, or they act surprised that they had similar technology to things we have now, or they think that aliens built the pyramids because obviously people who lived 3500 years ago weren't smart enough to build them themselves. It's the myth of progress *shakes head*