Indeed dried (prepared) cactus could be banned. But the trichocereus species are one of the most popular cacti to put in your livingroom (at least in the netherlands). Also there are a lot of succulent collectors out there who just grow the cactus as part of their collection.
They'll probably never ban the cactus itself.
They did with shrooms but who collects those or put those in their living rooms with only a couple of weeks of living.
Also cacti are not the most attractive psychedelics out there for most people. The taste, the myths and the poor availability. It's not that everyone will run out to the store to get some dried cacti and spend 36 hours and all the material needed for an extraction.
Mushrooms on the other hand were sold in souvenir shops here and are much easier to consume. Same goes for salvia. They are all just more available and easier to take to the general public
But when the ban is there who stops you to grow it yourself. The police won't bust your door for having some nice cacti in front of your window (a lot of old people will get busted here
). They probably don't even know how it looks like.
Scare tactics that's what they are, they can't simply enforce those laws.
It won't be banned because of people order some dry cactus over the internet. It'll be banned when mass media will cover it and youtube and alikes gets full of extraction vids.
Anyways I also grow them myself because I like to do so but I won't feel guilty in any way for ordering some dried cactus once and a while. I see it as my right of self-determination.