Probably the greatest injustice about random crits is that they will polarize good and bad players further. Whoever manages to lay the most shots down on the enemy will have the greater chance that one of those shots will be a critical hit. People who suck at aiming, such as new and bad players, will miss a larger percentage of their shots, and will be less likely to enjoy the odd advantages of a random crit. So by enabling this you're making the game statistically easier for whoever can land the most shots, on top of the fact that they already deal more damage with those more shots.
This is the only controllable factor in random rng, the only case where human pattern will promote different results. So basically you're creating an army of Halo needlers