I certainly wouldn't try to 'prevent' anyone from reading HP books or watching the flicks... I think it would be just plain stupid and an infringement of another's right to choose their own entertainment (so long as it is not harming another)...
However... That said...
While I don't think that anyone and everyone who watches a HP flick is going to run off and become a demon worshipping psychopath - which *rolls eyes* I've heard some (who should know better) claim - I do see the potential that a small number of the total number of viewers/readers will be influenced into thinking that magick is all fluffy, harmless bumpf... any serious practitioner of Magick will tell you that there ARE dangers... *shrugs* hey! I was a pagan (on the Left Hand Path) myself... (you can read a bit more about that at my site - link in my profile)
Now that I am a Christian I feel that it is only right (and a 'responsibility' - for want of a better term) to warn ppl of the dangers in Magick (both those acknowledged by practitioners) and those defined in Scripture... the old analogy of "If someone was in a burning house would you warn them to get out?" comes in here... yeah I know it's not a 'perfect fit' but few analogies are but I think you see what I'm getting at...
As someone mentioned in another Potter thread I think Harry Potter makes no mention of the Wiccan Rede, the Sabbats etc etc... but Wicca is not the only form of Witchcraft nor is it even the only form of Neo-Pagan Witchcraft... My old Coven did not practice the Wiccan Rede and in fact 'The Rite of Vengence' was officially accepted into the Coven's 'Book of Shadows'. This was even reflected in the Coven's Motto: "Sic Gorgiamus Alius Subjectatus Nunc" ("We Gladly Devour All those Who Would Subdue Us")...
I personally think much more is made of Harry Potter than is neccessary - others will disagree - but as I said that's my personal view...
But as I said above and I say it again so there is no ambiguity here - and I say this as one who was the High Priest of a Neo-Pagan Coven before coming to Christ... Harry Potter is NOT a 'training manual' designed to intruduce kids to Witchcraft!!!! AND... Reading the books or watching the filns does NOT mean that your child will become a demon worshipping, blood drinking maniac (as I have herad some claim)...
That said...
It does have SOME impact however... in much the same way as TV shows and movies like Charmed, The Craft et al...
When I was High Priest of a Coven here in Western Australia out of every 100 enquiries re Coven membership only a handful were NOT from teenaged girls who wanted to be like Willow from Buffy the Vampire Slayer or Shannon Doherty from Charmed... Yes it is a false view of Wicca and Neo-Pagan Witchcraft and certainly not what my Coven was about... but that's what they were after and to a large extent the likes of $ilver Ravenwolf and Fiona Horne catered for them and lined their pockets with the proceeds...
In much the same way, when Oberon Zell (founder of the Neo-Pagan 'Chucrch of All Worlds') is putting out stuff like this...
http://www.amazon.com/gp/product/1564147118/qid=1114144249/sr=8-1/ref=pd_csp_1/103-1025318-5910205?n=507846&s=books&v=glance
http://www.greyschool.com/main.asp
To say Harry Potter has NO effect ... well... it kinda rings hollow now-a-days...
I must admit that with Hogwart's being such AGGRESSIVELY protected trademark (HP fan-sites are always being shut down for copyright breaches) old Oberon has been quite clever in his presentation of his Hogwarts 'clone' "School of Wizardry" and - dare I say specific - in his 'target audience'...
Must be really miffed about all that lost income from potential CAW memberships that $ilver Ravenwolf and Fiona Horne nabbed by NOT larfing at those teen girls that liked The Craft and Charmed et al and wanted to be "just like Shannon Doherty"...