What you're describing might be acceptable if the airline were transparent about it: "This 90 person flight will be overbooked by up to 10 people. Based on data

What you're describing might be acceptable if the airline were transparent about it: "This 90 person flight will be overbooked by up to 10 people. Based on data over the last 12 months, there is a 5% chance one or more people in your party of 4 will be involuntarily forced to wait for the next flight, which is 3 hours later. That would lead you to missing your connecting flight, resulting in a total delay of at least 9 hours for your trip." Without this level of transparency it is impossible for me, as a single consumer, to make an informed decision about my purchase, because perhaps the most important part of the product--the likelihood of arriving at my destination at the time advertised on the website--is opaque to me. What's worse, there is a moral hazard here, as the airline is incentivized to overbook by as much as possible to eliminate any possibility of an empty seat on the flight, while they are not legally obligated to inform customers of the degree to which they are overbooking. The market only works when information is free and complete. When an airline overbooks by such a large margin, it's a breakdown in the air travel market.