With proper regulation we should expect some of the negative consequences to go down. Heroin deaths (for example) are largely related to illegality - unknown quantities and ingredients, contaminated equipment etc. Cannabis is considered a less harmful alternative to alcohol by many people.

In a social system like the one in the UK, I don't think drug users should be penalised over anyone else - taking ecstasy has roughly the same harm profile as horse riding. Do we tell equestrians we won't treat them?