As inequality is a guarantee - no two people are alike in any aspect and neither are their abilities as an employee - mandating (either by gun or union contract) lockstep equality in payments and job security, the highest performers are demoralized and put in the bare minimum or quit (if they can). The result is the ever-increasing shitty quality of the firm and its behavior. For modern examples see the NHS (bleeding doctors and nurses to the private sector) and American public schools in inner cities (highest global costs per student yet abysmal results).
There are valid criticisms about inequality but the pros far out way the cons.