Professor Alex Stevens:

Yes, this is a pretty murky area because there is a danger, as has been shown by recent examples in Canada, that criminalising use in public spaces while decriminalising possession, essentially criminalises people who are homeless, because they do not have anywhere else to use, and creates large inequalities between people who have and do not have private spaces in which to use these substances. On the other hand, it is fairly well established that people do not like to see people using drugs in public spaces. However, there are plenty of things people do not like to see happening in public spaces and the police are well capable of dealing with them without criminalising people. Through the use of park by-laws and moving people on, one can put a lid on the problem of public drug use without recriminalising people who use drugs.