No, I'm not talking about undead clerics on motorcycles, although I'm sure now someone's going to say "That's a great idea!" But in the discussions here and elsewhere about undead and level drain, there's been a couple comments touching briefly on the relationship of the cleric to the undead. As we all know, the cleric was added to the game specifically to counter an uncontrolled vampire lord who was dominating the game. The cleric exists specifically because the undead are very powerful and scary; if you neuter the undead, turning them into just another kind of monster with maybe an immunity to fear and mind control, there's no real reason to keep the cleric. Likewise, if you reduce or remove the cleric's power over the undead, you make the undead too difficult to deal with. It's like a little economy or food chain.
You aren't supposed to go toe to toe with the undead. You're supposed to run, or get a cleric to chase them off. Once you've acquired the means to destroy them at a distance, that's when you face them. If you take away level drain, you'd better replace it with something equally as scary, something that will make the players want to avoid the undead; otherwise, you've just made the cleric irrelevant and turned "undead" into a piece of fluff in the description.