I've read the book, and I'm still not sure wear the "gain killing" ideas come from.
The not doing the program sub-chapter seems to focus on hitting calorie targets and bar weight targets. Presumably "cardio" means you burn even more energy, but as long as you eat enough, I think it's within scope.
Your advice is solid though. Rippetoe focuses on increasing strength, so any other goals or constraints are up to the trainee.
I don’t believe it is in the books. I’d have to dig out the blue book and verify. But I think most of it comes from Rippetoe himself - forums, seminars, YouTube, etc.
For example, I went to one of his seminars in 2008 (I think. It’s been a minute). And someone asked about slow running in Maffetone zones, and he said paraphrased - “Look. You do what you want. But don’t come whining to me that your squat keeps stalling. I’m just going to tell you to stop running and eat more food”.
Depending on what you do for cardio, it will have an impact on the muscles. It’s not just calories. If you run/jog, the impact on your joints will accumulate with the lifting impact on your joints. And I think this is because beginners gravitate to Starting Strength. They try to do everything. They don’t know how to do things in moderation. So (IMO) it’s easier for the Starting Strength world to just say “No. Don’t do cardio”. Just some of the coaches are very, very draconian and less than flexible about it.
The not doing the program sub-chapter seems to focus on hitting calorie targets and bar weight targets. Presumably "cardio" means you burn even more energy, but as long as you eat enough, I think it's within scope.
Your advice is solid though. Rippetoe focuses on increasing strength, so any other goals or constraints are up to the trainee.