This is frequently solved by getting people to buy a food scale and weigh everything they eat for a few weeks and calculating the actual caloric content of their food. Food scales are frequently all people need to make real and persistent changes to their weight.
The biology isn't complex enough that ignoring CICO or telling people that it's wrong is useful or helpful and not harmful.
I agree, and believe this is part of it. People aren't paying attention to what they eat. This is specifically why understanding human behavior is important and that only repeating CICO is not useful.
If people are interested in understanding how metabolism regulation works and finds that it's useful in modifying their diet to help them be healthier, that should be encouraged, shouldn't it? If understanding how different foods affect hunger, insulin levels, diabetes, muscle gain, fat loss, I think that should be a good thing. If someone focuses purely on calories, they can easily deprive themselves of nutrients and hungry, making it hard to keep themselves on the diet and failing to get or keep themselves healthy.
Understanding CICO is sufficient to derive all useful, actionable advice for healthy weight management (e.g., maybe you're measuring wrong, stop eating calorically dense foods, eat foods that are more satiating, etc.).
Understanding the difference in how fructose is metabolised compared to glucose is majoring in the minors and is far less likely to help someone achieve their goals.
CICO is the most important factor and the simplest to understand. Suggesting people teach themselves biochemistry and physiology without understanding the basics is silly and far less realistic. Ignoring CICO is setting people up for failure which will discourage compliance and further improvements.
I believe you're misreading what I'm saying: I'm saying that only repeating CICO is not helpful. That itself does not give people the tools they need to be able to maintain health. You yourself point this out in saying it's "sufficient to derive all useful, actionable advice for healthy weight management": Not everyone is able to derive things from first principles.
Perhaps we're talking past each other. I'm more satisfied understanding human behavior and metabolism regulation than only repeating CICO and expecting people to derive everything else from there.
I'm certainly not against giving more advice than CICO and I'm not saying we should expect people to derive things from first principles, just that any method of weight loss that works will be working by CICO and understanding that is far more useful than not, and that it is outright harmful for people to suggest that it doesn't work.
I actually wrote a rather long comment a few months ago about my thoughts for healthy living in general if you wanted to know my thoughts beyond CICO: https://news.ycombinator.com/item?id=14681035