I agree in that celebrities' primary role is not to be a model for young children, etc. However, modeling behaviour after someone one admires is a common human behaviour--it establishes itself in infancy and early childhood as mimicry, and during those formative years it helps the young child adapt to a new and unfamiliar world by imitating the behaviour of others who are in the environment. This behaviour continues throughout late childhood and the adolescent years in subtler forms, normally, and the tendency to revert to mimicry persists as a successful adapting mechanism throughout the remainder of one's life.
The part of your post which states children and young people would be better suited modeling themselves after their parents/family members/people they are close to seems to function only under the assumption that everyone has good relations with parents/family and has people to form intimate/positive attachments with, or the capacity to form these attachments. This assumption, albeit benign, is a mistake. There are people who would be better off not modeling themselves after their parents (if I were to model myself after my father, I'd be 10 years overdue in child support payment and unemployed. If I were to model myself after my mother, I'd be a child-beater with a nicotine addiction. If I were to model myself after my non-nuclear family, the possibilities are endless: I could be an alcoholic, stuck in a deadbeat marriage to an alcoholic living in the worst part of town, a deadbeat son who still lives with his parents and is nearing 40, or a decent person whose only (perpetual) mistake is to continue to financially support her nicotine-addicted daughter. If we count people we used to live with, I could model myself after my stepfather and be a manipulative, vindictive, bipolar maniac.) So, as you can see, not all people have the option of modeling themselves after their parents/family in a positive manner.
When you've had a childhood like mine, your capacity to form healthy, intimate, and meaningful attachments with others is pretty much nil, so that's not really an option, now is it? The only thing that leaves is to substitute the attachments you would find within your microcosm of existence with people/things on the outside (and sometimes even abstract) world. This is where celebrities come in--people who are unfamiliar to you, yet so much a part of the outside world that they make themselves familiar people (it's an odd phenomenon, but that's the way it is.) It is not uncommon, then, to find people whose role models are celebrities. This "attachment" is usually borne out of nothing but admiration, and most of the time it is absolutely harmless. However, the danger comes when celebrities act in negative ways, as has been observed.
While I agree that their role is not to be babysitters, celebrities also ought to be conscious of the role they do play in the world--and it has far transcended that of entertainer. Simple observation would grant one that perspective. No one forced them to become a celebrity, so it would seem that this agreement to become famous comes with the burdens of losing one's privacy and becoming some sort of "model" attached. Does that mean they ought to be perfect? No. However, simple human decency is not much to ask for. There is no reason whatsoever why celebrities (or anyone else) ought to be drugging themselves up all evening, or giving people the finger at family events, etc. It's not logical, and of course they know it, and some do it for the attention.
Moreover, when a celebrity chooses to involve himself in businesses/industries which cater to children/adolescents, there should be a certain implied standard of behaviour because the audience is, on average, more vulnerable to messages sent out by the celebrity, even (or perhaps especially) outside of the professional environment. By choosing to work in things which cater to children, these celebrities are informally committing themselves to a more-or-less "clean" standard of behaviour, especially when they are minors themselves (i.e. Miley Cyrus in her Montana days.) Those celebrities, I would agree, have a duty to be good role models because they are involved in industries which cater to children and are representing that industry and its values.
Celebrities which are involved in adult-oriented (not porn, but meaning general entertainment) entertainment should not be held to the "role model" standards, but they should be expected to behave in a civil manner, like ordinary citizens.
Those are my two cents.
