Yes. Markets are a means, not an ends. When markets undermine basic fairness, they are gross.
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.