The pets I see being carried in the cabins are always well-behaved. It's a few of the humans who cause all the problems.
I'd think ~most~ little dogs that are used to going places would be fine... It's just some people who might be tempted to bring spoiled precious with them... or people with cats that I think might be a disaster often enough. Even my cat that travels pretty well will yowl if he's in the cage long enough or he's bumped around and tired of it.
So true. I took one of my yorkies on a trip to TX and she was perfect. All I needed to do was put my hand into her open carrier once in a while to reassure her and let her give her licks..and she would go back to sleep. Too bad it's so darn expensive. Cost me $180 for round trip from OH.