Edgar Ironpelt
Adventurer
I don't want them to get crits on undead, but I do want them to get their class damage bonuses (favored enemy and sneak attack). Critical hits are a matter of luck but those class bonuses are a matter of character skill and knowledge. I want that that sort of character skill and knowledge to have a high value in my game as a counter to the "Magic is trumps" attitude I see not just in 3.x but in the earlier editions of D&D as well.For me I never understood people wanting to find ways to let rogues and rangers etc get crits on undead. They don't have vital points in their anatomy, which is what a critical hit is searching for (especially something like a backstab). But I also don't reallyp rescribe to every class needing to be their most useful in every scenario, which seems to be where the sentiment comes from.
As for a rationalization, I use "the characters know that these things lack the usual mix of more-vulnerable and less-vulnerable points that living creatures have, so they don't angle to hit the more-vulnerable points in preference to the less-vulnerable ones. And knowing how to adjust their attacks this way gives them their class damage bonuses."