I know a number of people, including myself, who stopped smoking pot because they started to react badly to it.
I suppose it has to do with different body chemistries.
I also know people who react badly to alcohol.
And the majority of people in the world ( also including myself) are somewhat lactose intolerant.
I'm not about to advise people not to drink milk, though.
Smoking pot all the time is probabably not a very good idea - neither is drinking alcohol all the time or eating all the time. Everything in moderation.
ETA: Out of curiosity, I did a search for "cannabis" on the NHS website and all I could find were pages and pages about how horribly dangerous cannabis is. Nothing at all about its medical benefits.
Also, as someone who had a grandparent with schizophrenia, I'm offended by all the pages about how smoking cannabis "causes" schizophrenia. Schizophrenia is a complicated biochemical disorder with a genetic component. Cannabis may aggravate the symptoms in someone who is already beginning to develop the disease. People who are already experiencing symptoms of schizophrenia (which aren't just "hearing voices") may use cannabis to relieve them if they don't have access to medical treatment or if the medical treatment isn't working or has unacceptable side affects.
But you can't "make" someone schizophrenic by having them smoke cannabis.