First, these drugs aren't "hallucinogens". They're psychedelics (mind-revealing). A hallucination is a false perception which the person believes to be real; visuals are perceptions that the person knows are not real, such as "light shows". Except at very high doses, these drugs don't produce hallucinations per se. Other drugs can, but LSD and psilocybin generally do not. Ok, that may be a pedantic note but the term "hallucinogen" is incorrect and I think it's important to point that out, because much of the stigma associated with these drugs is the misconception that they generally produce true hallucinations (which are extremely dangerous, except for the kind that occur in the 8-hour-long catatonic state that the body and brain require each day).
Second, I'm 28 and I've known a lot of people who've used these drugs. The dangers are real. I'm not saying, "Don't do them." I am saying that if you choose to do so, you're on the frontier of something whose upsides are intensely personal and difficult to measure (this doesn't make them "not real", not in the least) and whose dangers are serious. Then again, so are the dangers of alcohol, which is legal and socially accepted.
It's important to understand, even though that attitude is mostly wrong, why society holds negative views toward this sort of drug use. It's because the upsides (positive personal experiences) are invisible except to the user, while the downsides (psychological damage) are quite visible and affect other people. Also, most of society sees absolutely no distinction between pleasure-seeking, stupid, and possibly self-destructive drug use (cocaine, heroin, inhalants, methamphetamine) and exploratory drug use (LSD, psilocybin). Most of us know that there's a world of difference between those two patterns of use and the types of people who pursue them, but most of society has no clue. They think people use LSD because it's "fun" and as a party drug, not as a means for growth.
Guilt and anxiety are two psychological hurdles to positive drug experiences. As for guilt, I explained why society considers drug use to be "morally wrong", not because that attitude is right but because one needs to understand it. If you've internalized it, it's something you're up against and need to resolve before you touch a single drug. You should examine your own morality and make sure you're 100% OK with what you're about to do. If you have reservations, don't do it. Don't ever use drugs because of "peer pressure" either, because it's always OK not to use drugs (you're not missing out on that much). But if you do decide to use a drug, don't spend a single second of thought on that guilt. It's now in your body, and it will leave, and there's not much you can do. But I'm prepared to say that, no, drug use does not make you a bad person. :) It may be unwise in many circumstances, but it doesn't make you "bad".
Anxiety is more of an issue. If you have issues with anxiety, depression, or panic, you should probably stay away from psychedelic drugs outright. This includes alcohol. I developed panic disorder in the least "druggy" means possible (working on Wall Street through a nasty throat infection that eventually put me in a hospital) and aside from an occasional beer (and I limit myself to one) I haven't touched a substance like this since then (that was March 2008). My PD is manageable at this point (about 2 attacks per month, with frequency and intensity continuing to decline) but I have no desire whatsoever to roll the dice.
I would also note that legal drugs exist. This is important because one of the worst things about some illegal drugs is that they are illegal; this is (1) conducive to paranoia and guilt, and (2) a factor that means you will likely have to form relationships with some pretty ugly people in order to get access to these drugs. So, if "breaking the law" is an issue for you, there are legal drugs out there. Psychoactive lotus is interesting and mildly psychedelic, and seems to be innocuous. "Mind machines" (not a drug) can have similarly interesting effects. Salvia I would advise people away from unless they know what they are getting into. Don't be fooled by its legality: it's extremely intense, and high-power extracts can produce a very unpleasant experience.
Ok, now some personal thoughts. If I had to describe psychoactive drugs in one word, it'd be: unnecessary, at least for most people. Their therapeutic potential really should be investigated by mainstream psychiatry, but I don't think most people need them in order to have powerful, beautiful spiritual experiences. There's an arrogance in certain drug-using communities about the power and singular importance of these experiences, mostly a reaction to society's (unjustly) extreme negative attitude toward their behavior. Those experiences can be interesting but are not a necessary part of a deep, spiritual life. Not at all. Really, a lot of people use psychedelic drugs and learn nothing. Timothy Leary was an outright mess (and an alcoholic) toward the end of his life. Psychedelics can certainly show what's possible, and that shouldn't be entirely discounted, but I don't think they're a good substitute for a true spiritual path that becomes a deep part of one's life, not "recreation" in 6-hour installments.
I've come to the conclusion that the effect of these drugs is to accelerate karmic processes 100- to 1000-fold, so that you mentally "age" a few months in a couple of hours. If what's ahead of you is spiritual growth, you might grow a little faster and have a very positive experience. On the other hand, if you're 3 months from a nervous breakdown that you might be able to avert (therapy) if you have sufficient time, drug use is a seriously bad idea because this acceleration makes said breakdown more likely to occur immediately and fiercely.
I think much of what gives psychedelic drug experiences their power is the duration of an open-minded state. If you have the skill and focus to hold a mindful, meditative state for one hour, much less 6, you will have a very potent experience-- probably much more meaningful than most drug trips. I don't want to give the impression that this is easy. It takes a lot of work and study to get to that level of skill. You've probably been meditating for months, if not years, before you can keep a mindful or meditative state for an hour. Once you develop this skill, however, it's very much worth it and you will have no need for (and probably not much interest in) psychedelic drugs.
One note I'll also point out is that the "failure mode" in meditation is non-experience, which is much softer a landing than the failure mode of drug use, which is an intensely negative and potentially damaging experience.
Ok, I'm done. I know that was long, but this is one of the most important decisions that young people face and most go into it without enough information, so I felt it to be worth the volume of text.