Robb Stark
King in the North
Because it's not about the magic - it's about something called responsibility!
You don't keep every person from drinking alcohol, just because there are support groups for it as it is potentially addictive and can turn you into an alcoholic.
Same thing with magic
That's not what I said, or at least, not what I meant. I said they should have stopped her from getting in too deep, not that Willow shouldn't do magic at all. Sure, Giles puts his books on the top shelf, but he doesn't exactly try to do much if magic is supposed to be that addictive. His speech in "Flooded" is really the first real time anyone says anything to Willow about it.
Plus, they completely throw the addiction storyline out the window in S7 with the excuse of "it's a part of her now". Um, come on. I like S7 a lot, but it stretches credibility quite a bit when you have an entire major arc about "magic is drugs" (which had already been changed from "magic is love") and then, simply because Willow would have nothing to do as a character without magic by that point, change it radically again. Almost every notable addiction program out there advocates abstinence.
I don't want to come off as negative, but Willow's magic arcs are one of the parts of the latter stages of the show that make me roll my eyes. I just felt like the storytelling got kind of lazy, and that wasn't an issue in the first three seasons.
I don't really understand your "It's about responsibility!" comment though.