I read a newspaper article that said , in essence, if cannabis is an illegal and unhealthy substance then the law should enforced. Just because stabbing in London is out of control, then a similar a argument would be to legalise stabbing- a ridiculous suggestion of coiy.
"Will legalising cannabis stop the illegal trade in other drugs?"
No, it will not.
Legalising Cannabis is, in my opinion, a bad mistake. It sends a signal to young people that it's harmless, and that's not true. In the short term it can affect your ability to drive. Some people experience panic attacks, and/or hallucinations. It can affect your ability to remember events and actions.
Habitual cannabis use can have long-term detrimental effects on health; the main one being a reduced ability to concentrate and learn.
I think there are two questions that I would like answered. Firstly, will it increase the use of cannabis? Second, will it reduce the volume of drug dealing? Very simplistic, especially on the second question, but if the answers are No and Yes, then it might work.