Cannabis can generally do a lot of things along the direction of what LSD can do, only it is typically a lot more fuzzy and LSD can go so much further and is better to depend on for hard trips. With something like cannabis edibles you can definitely trip, but it is also easy to just fall asleep on high doses.
Weed has been considered a gateway drug for a long time, probably because the threshold to take it is lower (it is considered much less extreme and more casual) plus it can demonstrate a lot of different kinds of drug effects like stimulant, depressant, dissociative, psychedelic, entheogenic and perhaps even empathogenic.
I did try weed in high school before I started trying more serious drugs in college, but I don't think it is a requisite before trying LSD.
People form a lot of ideas about these things before actually trying them, like trying mushrooms first because the trip is a couple of hours shorter and they may have been told things about it being a safer, natural drug. Personally I find mushrooms to be much more hardcore than LSD, something most people unfamiliar with the territory find hard to believe.
For similar reasons, I think a number of people consider cannabis to be an introduction because it tends to be lighter, the duration is shorter, and they can check if getting psychedelia and intoxication makes them anxious which would mean something for their disposition to trip on acid.
While I think that cannabis is not necessarily a bad introduction to anything, I feel people should be very careful about their preconceptions. They should realize that beginners can easily overdose on cannabis and this can make them terribly anxious, but that does not mean they are not the kind of people for psychedelia. It means cannabis is a drug of its own and there are traps to be avoided, that otherwise can complicate things in ways that don't necessarily say anything about you. Just about the way you (badly) approached it and handled it.
