I don't think any actor should be considered a role model. That's not what they signed on for, and it is a tremendous burden to bear. Even in being normal for their age, they are going to alienate fans if they are considered a role model.
Example: Johnny Depp is an actor but never has been a role model, which is good because he was a wild child. If he would have been a role model, many would have condemned him for acting normally for him at his age.
No kristen isnt a good role model. Anyone who is accused of doing drugs shouldnt be a role model.
The title of role model should be reserved for parents, loved ones, mentors and generally people who care in your well being and want to take on this role for you. Actors or celebrities should not get this title simply because they are in movies, on TV, in magazines, etc. Remember that their jobs are to simply entertain us.