Here's the thing.
The Franchise Tag is part of the FA system. It was bargained for, just as the rookie scale was bargained for. It all works together. Changing one part, changes another part. For instance: lower the number of years of a rookie contract, or raise their wage scale, or allow guys on rookie contracts to perform-out of their contracts means vets are going to get less money distributed to them relative to the younger guys. And the CBA has made it clear that the NFLPA is veteran oriented.
To just remove the Franchise Tag because it would make the players happy, is to dismantle a system in which the Franchise Tag is a key element of the entire system.
If the players want to bargain away the Franchise Tag, fine. But of course the Owners will want something in return. How about getting rid of guaranteed money, which to me is a HUGE deal for the Owners to swallow. How about players can never get more than 1 year of their contract guaranteed? Not suggesting it, just making a point.
Over time, this thing about players positions and what they are paid relative to other positions revolves and balances out. I remember when Oline was the red headed stepchild of salary structure. No more. At the moment, RBs have moved their way down the totem pole and of course they don't like it. But, as long as there are free markets and a salary cap, teams are going to have to make value decisions on which units/positions to spend precious cap dollars on; there is no way it can be equal for each unit/position. Prioritization is a basic business principle that will never go out of fashion because it is needed for success. And, as of now, RBs aren't a very big priority.
