There are more than sufficient airlines on major routes for competition (and you can see this when they get into fare sales for stuff like LAX-ORD for $50). Consumers could be flying airlines like Southwest and Virgin. The fact that they instead choose to fly on airlines like Frontier and Spirit shows that they don't actually care to spend the extra money to have reasonable seats or service.
I especially have to scoff at tech workers, who don't lack the money to make their travel experience more pleasant, but still take redeyes to save money and then complain about how much they hate travelling.
I feel like the people who are fighting for regulations on seat sizes don't understand that those regulations will cause ticket prices to go up. If you're fine with paying extra for a bigger seat, that's cool, but you can also already do that today (Economy Plus or First) without any political fighting. All you'll be doing is removing access to flying for the poorest people.
As for the safety issue, I'm no expert and I haven't seen the original complaint, but the FAA already has a regulation about the maximum time it can take to evacuate a plane (and therefore a limit on the number of seats per door on the plane, effectively). This hits the airlines with no first class cabin hardest, as they actually can't pack the entire 737 full of their standard economy seat.