Here's another reason not to discourage them: it would really suck for them if, ten years later, they still regretted not at least TRYING to get in. Basically, there are three ways things can go down for any pre-med:
1) Apply (once, twice, maybe more times), fail, accept it and move on.
2) Apply, get in!
3) Don't apply, always wonder whether maybe you could have gotten in if you'd applied, can't accept it and move on.
You want options 1 and 2 for your friends. Option 3 is bad. Spending $2000 and one year in futile hope won't be the end of the world if they don't get in, and they owe it to themselves to at least give it a try. Besides, being supportive is what friends do. Parents and adcoms are the ones who tell you you're not good enough.
Finally, you can also refer them to the MCAT vs GPA grid if you really want to give your friends a reality check -- I have a link to it in my signature. Their chances might not be as hopeless as you think, so you should check it out too.