I don’t think you will get any objections from airlines, if they are ALL forced to provide more legroom.
I personally don’t care if you fit a B767-300 with a 100-seat configuration.
The price of a seat WILL then rise. The only losers will be the majority of people who want to take a holiday and find that they can no longer afford it.
What the public really want is more room for free. They won’t be getting that. The economics don’t allow it.
The passengers themselves will be the biggest loser in this.