But let's be honest - in a horror film, they are a fairly important part of what makes them iconic, in the same way that great action set pieces make a great action film. Think the shower scene in Psycho, the corridors of blood in The Shining, the head in the boat in Jaws, the bloody prom prank in Carrie, the chestburster in Alien, etc, etc. The Exorcist's shock value-based visuals are an extremely important component (even though I'd argue they are actually quite restrained). Like the other examples I just listed, they are judiciously deployed, not overdone, and provide the electricity that charges the rest of the film.