I have an idea, maybe stupid, but it's the only one I have for the moment :
1) Let's gather all scientific data we have on entheogens, favorable and not favorable.
2) Let's gather historical data about prohibition (such as alcohol in the US in the 1920s).
3) Explain to what extent the government in Holland chose the right decision to make a distinction between mushrooms/cannabis and the rest
4) Gather actual statistics about psychedelics (people love statistics, they trust them) such as disease rate, mental illness rate etc.
5) Explain clearly why prohibition is worse than a regulated legalization
6) And in order to make people aware if those 5 previous point, the only way is to rely on mass media. Obviously, people will never let us broadcast this on the radio, let alone TV. So let's make a well-made video, something really well done, with fine graphics, well-chosen off-screen voice, fine off-screen music and broadcast it on Youtube, Dailymotion, and all sites that can support video and sound.
It's just an idea ...