>The flip-side is with baggage fees, passengers have incentive to sneak bulky baggage into the cabin, or carry the absolute maximum allowed amount of carry-on. This ends up forcing people to gate-check their luggage, because the cabin runs out of space. This costs time and annoyance.

Right, but that's an artifact of only charging for one of two "cost-adders", when they're close substitutes.

It doesn't refute the general point that it makes sense in general to charge more for things that add legit costs; the problem here is that they're not being consistent about it. Per previous discussion, charging for carry-ons seems to make more sense than charging for (a moderate allowance of) checked luggage:

https://news.ycombinator.com/item?id=13311317