I kind of like that because I'm SO annoyed with mages abusing it when I'm playing as a cleric with them. I partied with FOUR other mages in another KQ the other day and THREE of them abused life tap. Really annoying because I can't tell when they're life tapping or they suddenly got hit by a bunch of mobs. /sigh Life tapping abusers make me rage all the time.
But of course, like you said, it'll have to be somehow balanced.. probably a big CD on it.. though I've never been into those balancing class things so I wouldn't know... but if it stops me from healing life tappers, then I'm for it