I voted that cannabis is a malicious master.
Malicious is not the first word I would have chosen, and like all things there correct use and incorrect use, and similarly suitability of usage will differ between individuals.
I do however notice a fairly clear pattern of effect on many habitual users-
-Making connections that are not sensible.
-Seeing things, particularly political or moral issues, in black and white.
-Inability to recognize the above two manifestations as being a product of cannabis use.
Other effects which may be the product of cannabis + youth-
-Sloth
-Suggestability
-Use of cannabis symbols
I don't believe that cannabis' "spirit" has an agenda, or at least not an agenda as we would know one, but it does have an assertive presence, and perhaps that is why some people, as they grow up and come to know themselves, begin to find cannabis disagreeable.
Certain other people, because they either have particularly uncluttered or purified minds, or they have particulalry strong agendas of their own, can habitually use cannabis without become subject to its personality.