Alcohol cannot have complex effects on human personalities. Just the same as banging your head. Why? Well, the alcohol we drink is one fairly simple molecule. It doesn't have information about human personalities, and thus couldn't target parts of one. And it's not evolved in that regard (no selection pressure).
But couldn't it just happen to be the right thing to have one specific effect?
Well, first off, now you're explaining things by "maybe the world just happens, by luck, to be just the way I thought it was."
And secondly, if it only takes something as simple as alcohol (the molecule isn't many thousands of atoms, just a few) to make people more liable to cheat on their girlfriends, then why haven't we yet designed a chemical to make people act more chaste?
Thirdly, people are very different, and store information in their brains differently. They vary so much as to confuse scientists, so what are the chances a plant happened to grow in a way to work on everyone (including past people, even).
Genes also lack the information to complexly effect one's personality.
Genes also never got a chance to evolve this ability, because once people had personalities and there were selection pressures on them, memes, which evolve much faster, would always do it first thus removing the selection pressure.
And again, it would be quite a huge feat of luck for some gene to just happen to have the right qualities to effect the personalities of many different people.