...Must...Not...Go...On...Objectivist...Tirade...
Ahh, I'll succumb anyway. I don't have anything better to do.
Chrisp, it's almost glaringly evident that your logical fallacy (And I'm addressing specifically your claim that (and I'm paraphrasing (And using way too many parenthesis)) everyone should try hallucinogens because they will gain more insight into the world) emanates from the violation of the law of identity. A is A. A can not be B, because A is A. Existence exists, and nothing else exists. Similarly, you can't gain insight into reality by having an experience outside the realm of reality. You may learn more about hallucinogens, sure, but you do not gain more knowledge about the real world, because definitionally, you are not perceiving the real world.
On the broader subject of drugs, I consider drugs (Of all kinds, and I AM generalizing, and would say this of a drug that created pure happiness with absolutely no side effects) to be evil because they, in one way or another, alter your reality, by creating artificial happiness, sadness, numbness, etc. The defining charcteristic of mankind is their ability to think logically. Since a drug alters that ability, the use of a drug, at least temporarily, makes you less human.
If it were possible (And I will discuss this later) I suppose a drug that made you think more logically wouldn't be evil, as it enhances your human qualities, as opposed to diminishes them, however this is relatively impossible, since there are no degrees of logic. Logic is not a quantitative variable, but rather a qualitative variable. Either a statement is logical, or it isn't. I suppose it would be theoretically possible for a drug to cause someone to think logically a higher proportion of the time, but I'm on a huge tangent as it is anyway.
</objectivist>
My final objection to drug use is on the grounds of the relative depression theory of psychology, in which I am a big believer. For those of you that don't know, relative depression essentially states that you evaluate the happiness of every experience relative to your other experiences, ie if I go to a theme park one day, I will not be as happy the next, since I did not go to a theme park. Ultimately, I think this is what addiction comes from (And the science supports this). When your brain is overloaded with endorphins, it begins to think that any less than that level of endorphins is sadness.
At any rate, I've made my points. And this is a rather abrupt ending, but I don't really care. :-)