The link between cannabis use and psychosis is very real, although it's less clear if cannabis causes the psychosis. Other people have come to different conclusions than the paper you linked.
At this point there it's hard to be sure one way or the other, but all things considered I feel there's enough to warrant some caution (also wrt. dependency and some other issues).
Correlation is not causation. There are plenty of other drugs (especially alcohol) used for self-medication that are also linked to psychoses, as well as non-drug behviours that are strongly correlated to psychoses. The immediate jump to causation is mostly politically-based and not scientifically-based.
Yes, I believe I said this: "it's less clear if cannabis causes the psychosis". But thank you for your platitude.
The only answer which can be given with any certainty at this point is "we don't know", which may optionally be followed by "but I think that [..]". There is no "immediate jump" to causation; the only such jump I see here is dismissing things out of hand on account of allegedly being "politically-based".
> The only answer which can be given with any certainty at this point is "we don't know"
It might be a little more convincing if you shared whatever studies you're referencing to form this opinion, because while I don't have access to the paper linked above the abstract pretty definitively seems to be saying that we do know with some certainty:
> Evidence reviewed here suggests that cannabis does not in itself cause a psychosis disorder. Rather, the evidence leads us to conclude that both early use and heavy use of cannabis are more likely in individuals with a vulnerability to psychosis.
>Future research studies that focus exclusively on the cannabis-psychosis association will therefore be of little value in our quest to better understand psychosis and how and why it occurs.
The full text is on Sci-Hub; I won't link to it here directly (I'm not sure if it's allowed?) but it's the first result in popular search engines for me.
At this point there it's hard to be sure one way or the other, but all things considered I feel there's enough to warrant some caution (also wrt. dependency and some other issues).