Choosing The Grand Ole Opry over Trek? Damn...the mind boggles. Maybe Trek needed an episode that would draw everyone in. How about the Trek crew get bored and stage a pie eating contest?
I do seem to remember Laugh-In being previously connected to Trek's timeslot troubles . . . had no idea Jerry Lewis was on that show though.
Cushman makes the case that NBC hated Roddenberry's refusal to become a yes-man, his abrasiveness in dealings, and his insistence to follow his own vision for the show, and hence would be very happy to rid themselves of him. They had a much friendlier relationship with the producer of Laugh-In, so they were more likely to be nice to him than Gene. So Laugh-In got to keep it's Monday 7:30 spot, and Trek got the Death Slot (which is also a nickname I had for a girl I dated in high school).
Said it before, I'll say it again: the people who run network television are, and always have been, idiots.
"Laugh-In" was pretty iconic in its own right, launching Lily Tomlin's career ("One ringie-dingie ... two ringie-dingies") and giving us now-classic bits of pop culture like "Verrrry interrresting ... baht also stooopid."