What's the point? If people were willing to pay more, airlines would make seats bigger. But people want cheap flights, so they get small seats.
That doesn't mean that it is a safety issue.
> Nobody died in a crash of a United States-certificated scheduled airline operating anywhere in the world in 2016...it is the seventh straight year that nobody died in a crash on a United States-certificated scheduled airline operating anywhere in the world.
https://www.forbes.com/sites/danielreed/2016/12/28/in-the-la...
Also, evacuation after a crash is not the only safety issue - there is deep vein thrombosis, for example.
http://www.slate.com/articles/news_and_politics/explainer/20...