I think at some point putting 250 people in a bus or a 737 is a safety concern.

However, the problem with measuring minimum seat size by "pitch" is not right. The thickness of the seat is a huge factor that pitch does not account for. The ultra slimline seats on frontier actually give plenty of legroom with less pitch. I've sat on both united and AA economy recently and it's unquestionably less legroom than frontier. Comfy seats, but terrible legroom.

The FAA simply can't go with pitch, it's a bad metric to use