There were a lot of really strange movies that came out in the early 1970s----
The Exorcist, of course, and
Rosemary's Baby; but there was also
The Omen, and
The Wicker Man, and
The Possession of Joel Delaney, just to name a few. And those were just the ones that weren't straight-up horror movies (like
The Texas Chainsaw Massacre, for example), but ones that had demonic or satanic themes as part of their main shtick.
You couldn't be a teen or pre-teen in those days without having some exposure to these films, even if you didn't sit down and actually watch them; they were advertised everywhere, and the big blockbusters were endlessly analyzed and discussed. I was still young enough at the time to be scared to death of even the commercials for these things, and avoided anything to do with them. It wasn't until I was in my late twenties that I watched some of these, just to see what all the hullabaloo had been about. By that time I was mature enough (and had been exposed to enough
real-life horrors from my military service) that I could evaluate them objectively.
Most of them were creepy, sure; many of them were pretty tame, by today's standards; and the vast majority of them were just plain stupid. I remember there were Lovecraftian-themed movies starring guys like Dean Stockwell that were petrifyingly moronic, and there were scads of vampire movies brought out by directors trying to cash in on the fad of updating Dracula for the Pepsi Generation and make him like, cool and totally groovy, man, can you dig it? Most of the characters in those movies looked like they'd stepped out of the 1970 Sears & Roebuck catalog, with their stack shoes, wide bell-bottomed striped pants, five-inch wide leather belts, and turtleneck sweaters or flowered shirts with silk ascots worn under blazers with mismatched color stitching and brass buttons, like wow, totally copic.
I guess the one takeaway you can get from this is that there were really bad movies in the 70s the same way there are really bad movies today; but the bad movies in the 70s were shown in drive-ins or in late-night runs at rural movie theaters, while today, they run them endlessly on pay-per view streaming services.