As humans, we seem to have an instinctual desire to seek out experiences that alter our normal awareness.  We like the mental shifts that occur as a result of drugs, alcohol, sex, meditation, performance, ritual, exercise, and other activities.  These are essentially waking dreams, a counterpoint to the necessary dream state we experience during sleep.  While it's entirely possible to go through life without ever experiencing any sort of "high" or deliberately induced shift in awareness, the desire and capacity are built into us.  Each vehicle takes us to a slightly different place, so when entire paths are dismissed as being unnecessary for creating an altered state, I think it dismisses a state that can't be reached any other way.  For example, the mental states reached by sex and drumming are both altered from normal awareness, but they are not necessarily the same.   

To refer back to one of the arguments made regarding entheogens , some people dismiss the use of sacred plants in a spiritual context altogether, preferring to reach an altered state through less invasive means, like drumming, breathwork , dance, or meditation.  While these techniques certainly have their place and valuable uses, they will not always be the correct tool for every job.  Not everyone's nature is suited to those techniques, either; the Mysteries that animate those techniques are no more "equal-opportunity" than the Mysteries of the knowledge of sacred plants.  While I make use of many ways to alter my awareness (such as ritual, drumming, sex, meditation, seclusion, trance-possession, and chanting), the mental state I arrive at varies depending on technique and gives me access to a particular set of Mysteries that is best suited to what I wish to achieve. 

One of the most dramatic ways that entheogens are useful in a way that other techniques aren't is the way that entheogens can be used to alter the awareness of ritual participants, or the person who the spirit worker is assisting.  Several other consciousness-altering techniques are very insular, affecting only the practitioner (such as meditation); other techniques can potentially involve others, but depending on the person, not everyone will be affected the same way, or at all (such as drumming).  Ritual and ritualized drama have the potential to change the awareness of everyone in one way or another.  Entheogens can be used by the practitioner alone, by the practitioner and participants, or by the participants alone.   

Giving entheogens to ritual participants or to someone being healed is well attested to in traditional use.  Entheogens often play a part in initiation rituals and coming-of-age ceremonies, and help mark the transition from one stage of life to another; the chemical and spiritual effects of these plants can create a forgetfulness of the body and even identity, leaving the sensation of having died or changed in some way.  The shaman who facilitates this experience takes on a role of guide.  Their job is often that of sacred performer, someone who embodies the themes and images important to their culture in order to play on that importance in the mind of the person in a trance; this work is often criticized in outsider's accounts of traditional shamanism, the theatrical element being dismissed as nothing more than slight-of-hand conjuring to fool an aboriginal audience whose lack of "real" education leaves them open to exploitation.  The line between the concrete reality of the ethnographers and the intangible world of the shaman has been generally seen as incompatible, though when it comes to dreams, drama, and visions, reality is much more fluid than many people expect.  One person may have a dream that changes their life, thus altering their reality; how that importance is accepted by others depends on the value they place on the validity of the intangible and personal.  In the case of the shamans pooh-poohed by ethnographers, the importance of an individual's intangible world was emphasized and accepted as valuable.

The use of such "illusion" in trances has a very real, very important place.  Ritual drama brings the abstract into the realm of everyday life.  Presenting a person with a pebble that is a dart shot by an evil magician validates the pain and reinforces the removal by the shaman; in many cultures, if no such evidence is provided, then nothing is thought to have happened.  Giving deities and spirits a physical form by means of portrayal by actors brings those forces to the minds of those watching the performance.  We are all familiar with the experience of watching a movie and forgetting for a time that we are sitting in a movie theater with dozens of strangers; this sensation is called suspension of disbelief and for a moment the characters are real, not the projected images of actors.  In sacred drama that involves deities and spirits, for a few moments those entities are present to the audience.  When they perform well, the performers also experience a shift in awareness and are able to enjoy their work from a new perspective. 

Under the influence of an entheogen , the mind is very soft and open to influence; normal thought process is suspended and what amounts to hypnotic suggestion can be used to reinforce the idea of healing, of transition, or of whatever else the trance is being used to achieve.   Giving a dose to the person who is being cured or assisted is well known, and sometimes is the way a particular entheogen is typically used.  When properly given, the right dose has the potential to put a person into the correct space to allow you to perform deep healing or other work that would involve the altered awareness of a client.  Giving an entheogen , however mild, to another person is very risky business.  You can have no idea of their body chemistry, allergic reactions, physical or mental tolerance, or emotional stability when under chemical influence; it doesn't matter how well you know them, there will be things that they themselves are unaware of and won't be able to tell you.  The only exception to this would be if they could tell you what and how much of a substance they use, or if you are a professional medical practitioner; even in these cases I would caution against it unless you are very sure what you're doing.  Though several entheogens have little or no toxic chemistry, you will still be dealing with someone in a very vulnerable state; even with the best intentions, trouble can arise any time we are dealing with the internal landscape of another person.