http://www.thelancet.com/journals/lanpsy/article/PIIS2215-03...
But it states that there is a well established link between cannabis and psychosis.
The article you linked examines psychosis outcomes after quitting marijuana. It does not show evidence that psychosis is caused by marijuana.
In fact, the article is similarly misleading, as it makes reference to two studies which show, in the article's words, a "link" between psychosis and cannibus use. However, the two articles cited for this assertion [0][1] similarly only discuss a correlative link between psychosis and marijuana.
While the correlative relationship between marijuana and psychosis is well established, there is anything but a consensus for the causal relationship between illness and marijuana.
As they say, correlation != causation.
Edit: furthermore, I encourage you to browse the wikipedia page [2], which supports my assertion with multiple sources: neither consensus nor causal link has been established. You are spreading potentially harmful misinformation.
[0]Arseneault, L, Cannon, M, Witton, J, and Murray, RM. Causal association between cannabis and psychosis: examination of the evidence. Br J Psychiatry. 2004; 184: 110–117
[1]Stepniak, B, Papiol, S, Hammer, C et al. Accumulated environmental risk determining age at schizophrenia onset: a deep phenotyping-based study. Lancet Psychiatry. 2014; 1: 444–453
[2]https://en.m.wikipedia.org/wiki/Long-term_effects_of_cannabi...
If something that attacks your lifestyle or a dependency of it and you can not bring arguments forth, this does not give you the right to silence the debate.