Allowing homeless people to sleep and sex workers to work and drug addicts to use defeat the purpose of having a public space, because it essentially scares away all the non-homeless/prostitutes/drug addicts.
We are all supposed to care for the less unfortunate, but it doesn't mean a public park should be dedicated to them, not to mention the surrounding area will continue to be a dead zone no sane person would want to be anywhere close to it.
1) Homeless people should never be allowed to sleep in parks. Period. Why, because parks are not for that purpose. It is not like all they do is sleep. Many will urinate, defecate, having sex and use drugs there too. If I am not allowed to do those in a park, nor should they.
2) Drug addicts, if they insist so, should use in their own home and at their own expenses. I don't want to see their sunken faces on the streets. Just don't even show them. Drug abuse should always be considered a sin and a disgraceful thing. Drug users should always be discriminated against. Society should never degrade to the extent that we actually "facilitate" drug use.
3) As to sex workers, I am fine with their existence and don't discriminate them, but it should be regulated by the government. I am not against having a red light zone, but it doesn't have to be Moss Park. What about the financial district? It is a ghost town outside office hours anyway and the two complement each other perfectly.