I just put a HoT on those with low health or something... cba with all the hassle. If they're bad they'll never learn and will simply thing you're a bad healer, so what's the point. If you don't let them die chances are the boss will die sooner, making your run faster.
But yeah, I've given up on trying to teach them baddies a lesson. Such a wasted effort.
To those spouting some sort of retribution for the wrongs of having to heal someone (fancy that...a healer having to heal!?) remember this:
Theres you and the idiot you're refusing to heal...and then there are the 3 other people who queued patiently for 20 mins to run the instance. Fair enough, if the whole group are mentally subnormal, thats fine, be an ass to your hearts content. For the other 99% of the time, think of the group. We can't all insta-que