Passengers that treat crew terribly are essentially allowed to because the airline probably won't back their staff up and support any decision made by the people they employ.
Pile of rubbish. My airline deals with about 400 similar incidents a year and we back the crew every time (so long as evidence supports that the crew acted in accordance with their procedures and training). Every other UK carrier is exactly the same. It doesn't stop the rate going up each year, society is changing and people are becoming more belligerent and less accepting of being instructed.
Can you share what your experiences are of carriers failing to support crew when passengers have broken the law, and the crew have acted in accordance with their training? And you can't use that Korean peanut one, that was quite the anomaly!