I can't say much for any other hallucinogens, but me and my friends tried salvia for the first time a few months ago, and boy, does it make you trip BALLS.
I would go into detail about what I saw but that would take far too long, all I'm going to say is that my conscious mind had no control over what I was seeing, hearing or feeling even with my eyes wide open. Friends said I looked right through them as if they weren't even there and started talking in incomprehensible slow-mo style gibberish before I finally just fell backward through a plastic table in my back garden and remained motionless for about 5 minutes before coming back to reality.
While I was caught up in that experience, it's hard to explain the pure horror I could have sworn I was seeing before me with my very own eyes, but I'm sure it will suffice for me to say that I honestly thought for a moment that all of the reality we know had instantaneously been snatched away by some Godly, apocalyptic force of unfathomable proportions. I saw (what I thought was) the very last seconds of my reality (what I could see with my eyes) being TORN APART before me (by what looked like small, metal spires piercing through the image of what I was seeing), I'm not exaggerating this in the slightest, it was easily one of the most terrified states I've been in throughout my whole life. I ran into the kitchen and started eating and drinking food after my trip because I wasn't sure what was real and what wasn't..
Mind you, salvia is LEGAL.
Why?
I haven't got a single fucking clue, I guess the reasoning is that you're so fucking out-of-it when your tripping that you couldn't be any harm to anyone.
After hearing some other peoples experiences with it, I've heard that it induces hallucinations much more vivid and overwhelming than LSD or even Magic Mushrooms.
Personally I think hallucinogens should be illegal, or just very highly regulated and can only be used under specific safety measures, anywhere else, and it becomes a risk to you and others around you.