No certainly not. I do apologise as I didn't word that properly.
I meant that it is hypocritical to treat the user of a more harmful drug different from the user of a less harmful drug.
Drugs should be regulated according to the harm they cause to the individual and society.
Thus, the most harmful drugs like heroin, speed, alcohol and tobbaco should be most heavily controlled.
Safer drugs such as cannabis and MDMA should have less controls placed on them.
And montage if you read The Misuse of Drugs Act you will find that is the purpose of the law. However The Misuse of Drugs Act is not being applied properly by parliament, because both tobbaco and alcohol fall under its ambit.
Incidently the two drugs you mention, diamorphine and amphetamine are both used medicinally for many things, for eg. diamorphine for pain and amphetamine for ADHD.
Heroin is also a very bad example. People under the influence of heroin do not cause serious harm to innocent bystanders. Heroin addicts generally cause harm to themselves and others when they are trying to get their drugs. In Switzerland this problem has been successfully dealt with for 15 years by legalising heroin on prescription
The drug that is most likely to make Thomas the Thug cause serious harm to an innocent bystander is ALCOHOL and that is legal.
A good start on this topic is to take a look at the lancet graph on the relative harm of several different drugs.
So Thomas the Thug who dabbers in a bit of harmless cannabis, but one day decideds to try a bit of heroine or speed,
If you're talking about
http://en.wikipedia.org/wiki/Gateway_drug_theory it's been disproved time and time again but if it exists there are two problems here.
1) The first drugs people tend to try are alcohol and tobbaco, thus they're the gateway drugs
2) In an illegal market, a drug dealer will sell people anything. There are no controls on use, they will sell and do sell to children, and if there isn't any cannabis available, then they will push harder drugs upon people. There is a simple solution to this.