I think the concept of letting people with enough money get to do whatever they want is a bit unsettling.
People with enough money can already just buy a second seat or pay for business/first class.
This actually opens up increased comfort options for those with less money.
This is also a part of the game to avoid listing high fares on affiliate travel sites but then charging more through upcharges like this in an attempt to mask overall increases to average fare prices.
If it makes you feel any better there's not a single flourishing command economy anywhere in the world right now. China, Cuba, etc. are all moving towards market systems for a reason.
If history has taught us anything, it's that humans will create power gamification in all situations. The market system is the only way to harness those instincts to a somewhat greater good.
Planes are perfectly capable of flying without first class sections.
Markets where some players have considerably more coercive power than others don't tend to produce good outcomes.
The other consideration is that you'll likely not fill an entire plane if totally filled with economy seats so the price for everyone on an all economy flight would have to pay significantly more per seat to make up for the 60-80% capacity on basically 80% of routes.