Every argument you have that challenges marijuana is immediately nullified by the fact that we are allowed to abuse many substances that do even worse, especially when the one that has been made illegal isn't fatal, has mental and physical benefits and is being constantly proved acceptable and convenient by the places it has been legalised in. Legalising cannabis could bring in £900m in taxes every year, save £400m on policing cannabis and create over 10,000 new jobs.