Felon said:what is a "crit" exactly?
Apparently you are confused.
SRD:
Critical Hits: When you make an attack roll and get a natural 20 (the d20 shows 20), you hit regardless of your target’s Armor Class, and you have scored a threat. The hit might be a critical hit (or “crit”). To find out if it’s a critical hit, you immediately make a critical roll—another attack roll with all the same modifiers as the attack roll you just made. If the critical roll also results in a hit against the target’s AC, your original hit is a critical hit. (The critical roll just needs to hit to give you a crit. It doesn’t need to come up 20 again.) If the critical roll is a miss, then your hit is just a regular hit.
A critical hit means that you roll your damage more than once, with all your usual bonuses, and add the rolls together. Unless otherwise specified, the threat range for a critical hit on an attack roll is 20, and the multiplier is x2.
Exception: Extra damage over and above a weapon’s normal damage is not multiplied when you score a critical hit.
Increased Threat Range: Sometimes your threat range is greater than 20. That is, you can score a threat on a lower number. In such cases, a roll of lower than 20 is not an automatic hit. Any attack roll that doesn’t result in a hit is not a threat.
Increased Critical Multiplier: Some weapons deal better than double damage on a critical hit.
Spells and Critical Hits: A spell that requires an attack roll can score a critical hit. A spell attack that requires no attack roll cannot score a critical hit.
Also, just because you feel that crits are not well defined, and dont have an in game meaning (as well as out of game) it does not mean that it is so.
Crit range stacking is fine according to the numbers. It is fine to have a flavorful way in character to do certain actions (no different than being better at sundering really, or any other special action). It is not unbalanced.
So, in other words, no reason to disallow it.