How much would it change the dynamics of the game to have criticals not require confirmation? I would apply this universally, both for the party and the monsters.
It would significantly boost weapons with a wider critical threat range above and beyond weapons with a higher crit multiplier.
It would be fairly strong, and it is sometimes even a capstone for a class.
The power this adds to full attacks comes not from your high BAB iteratives, but your low ones. Let us take a longsword (19-20/x2) on a level 6 fighter (+6/+1 full attack). You roll a 19 on your 2nd iterative. You need 20 to hit (let us say he is attacking an unbuffed wizard), and you just barely make it.
With a confirmation roll, rolling anywhere from 1 to 18 would just mean this is a normal hit. Without confirmation rolls, this is automatically a crit. So you turned a 10% chance into a 100% chance. And things get even crazier with things like keen rapiers (15-20/x2).
Now, while it might seem fair to have both sides get this amazing power (just turning melee into rocket tag)... but mostly, this just punishes casters. They rarely benefit from it (ray specialists?), and they suffer more since they tend to be more fragile. Now, whether casters need to be punished more often is an entirely different issue.
Plus, it means that there will be a high fatality rate at level 1. When just about everyone dies with 1 crit... that is a 5%-15% chance of dying whenever you are hit. And this high death rate lasts for a few levels.
Critical confirmation exists in order to reduce the 'swingyness' of combat. Swingy combats favour the weaker party, which is almost without variance the monsters, not the PCs. Thus, by removing confirmation you are making the game less predictable (which is bad) and making fights harder for your players, in a way which is difficult to moderate (which is bad).
A lot of people remove confirmation rolls without really understanding why they are there in the first place. I would think very carefully before you do this.