Pop rushing exists because it's an interesting game mechanic that interacts with conflicting goals around population growth, happiness and unit or building production and has some elegant inherent trade offs between different short and long term goals. I will under no circumstances remove or replace the mechanic as is. It is deliberately associated with a civic that is broadly historically applicable to all eras in history because the player always wants the option to use it so doing so is meant to be plausible throughout the entire game. Furthermore, its powerful effect is placed in a category where it competes with other powerful effects to make its use non-obvious. It's just a game mechanic after all and best looked at more abstractly. It's only because of the vanilla game that you associate this so literally with slavery.