But who has the right to give me a story that's incomplete and expect me to like it?
Ummm, anyone who's ever made a movie based on a novel? Those invariably trim out huge amounts of content, because adapting a full book would take a whole miniseries' worth of time. (Even Peter Jackson's extended cuts of Lord of the Rings
leave out a bunch of stuff from the books.)
There's also Reader's Digest
and other publications over the generations that have presented condensed versions of novels and stories. Those have been very popular for a long time. A lot of people want
shorter versions of stories because they only have so much time to devote to reading. A condensed version lets them get the essence of the story more efficiently, and for some people, that's desirable. So don't go spouting self-righteous rubbish about your "rights" being violated. You just have different tastes from the target audience, that's all.
Abridged was awful and I never bothered with the Star Trek audiobooks because S&S didn't care enough to do it right.
You're forgetting, this was before digital audio, and you could only fit a finite amount of content on a cassette tape. It's the same reason movie soundtrack album releases back then were incomplete -- there just wasn't room to be comprehensive. They weren't cheating anyone out of anything, because it wasn't practical to do an unabridged version in the first place; it would've filled up too many cassettes and been too expensive. It didn't really become a practical idea until the age of digital media and downloads. S&S did the best they could given the technology and the market of the era.