Excuse me, but isn't Energy Drain a 9th level spell?
So...you don't mind Prismatic Sphere (makes you nearly impervious to people without Disjunction), Mordenkainen's Disjunction (destroy permanent magical items and artifacts), Time Stop (ultimate combat spell), Imprisonment (goodbye forever, no save), Wail of the Banshee (kill everyone) but yet you have a problem with Energy Drain.
Energy Drain? When a cleric half your level can undo the damage you've wrought?
If it's from a inconvenience point-of-view, this is a ridiculous objection. After all, creating a new character is much more arduous than merely levelling-down a character. And raising the dead is more difficult than merely casting restoration- and using freedom is far more tricky than either (spell level-wise).
If it's from a mechanical problem of when the PCs are restored, just jot down how much XP they've lost. When they get restored, this amount of XP is recovered (or a proportion thereof, for Restoration as opposed to Gtr. Restoration).
If it's from the point-of-view that it's mean, let me let you in on a secret. Levelling down is no more 'unpleasant' than dying (unless you're level one perhaps). Finger of Death (7th level) causes permanent DEATH, and Disintegrate (6th level) goes one better. Energy Drain (9th level) merely level drains you, which nowhere near as bad. So this isn't an argument either.
With these three arguments destroyed, who can't like Energy Drain?