I agree, and I made the exact same argument with the folks who have a problem with it. It has been a policy of the group from very early...but it was never called a "core value", until we started doing so in our pre-GA patter. It's semantics, and I agree that the "no drugs and alcohol at the occupation" was consented to very early on. But, people are bothered by calling it a core value, since when it was passed, it was not referred to as a "core value", and never has been called that until facilitators started including it in the spiel at the beginning of each GA. Facilitators have occasionally caused ire with this sort of thing, and I'd like to avoid that kind of accusation now. If the GA consents to call it a core value, I'll call it a core value. Until then, I plan to keep mentioning it, because I think it is important and I think the GA still believes in it, but I'm going to call it something other than a core value. Perhaps similar to "step up, step back".
Our "core values" statement, which was consented to at GA only has three actual core values, and "no drugs and alcohol" is not one of them; the fourth value is more of a recommendation to future GAs that the core values should only be changed in solidarity with the movement as a whole..which is pretty difficult to fit into a pre-GA spiel.
If you have another preference for how to phrase it, or how to more accurately remind everyone of this GA-consented guideline without calling it a core value, I'm happy to hear it.