They never do. When I was a kid I saw the 1953 movie "Invaders From Mars" on TV, and was terrified by it. Had recurring dreams. When VCR's came out, I got it on VHS, watched it, and couldn't understand why it had bothered me so much.
Oh yeah - the original Invaders from Mars. I saw that on tv also and I was freaked out for ages. I think it was because of the ending when the kid wakes up, having dreamed it all, only to have the same UFO land in the sand pit, just like the dream. Brrrr.
The Crawling Eye was another. And Rodan for some reason. And the one where the head of the girlfriend is kept alive in the lab after the bad car accident. I’ll stop now, because I could go on....and on.