I think we should first get over some urban myths that plague this issue.
A drug addict is not automatically a dangerous person, either to himself or to others. Jumping into the driver seat of a car while under the influence won´t automatically mean you become a road hazzard. Actually, the greatest ammount of accidents caused while under the influence of drugs, are caused by recreational users, not addicts.
After a few months of consumption, an addict will have a very hard time getting "high". He consumes drugs just to feel "normal", and take away the pains and akes of cold turkey.
When i first started using heroine, it took a simple dose of the stuff to really be in cloud city. During that time, i was a REAL danger while on the road. My vision would blurr, my reflexes were down to a crawl, i was an accident waiting to happen. But a few months after, when the addiction starts to kick in and you pass from a recreational user to an addicted user, you would be hard pressed to find anything abnormal with me if i was under the influence.
Infact, i was a bigger menace while on cold turkey than while i was "high", so to speak.
Addicts don´t take drugs to get high anymore, they do it to be able to lead an almost normal life. The same drug that before caused me to act abnormally, is now helping the addict to just cope with daily life. It assumes the same part as insuline does to a diabetic.
After the first year of regular useage of heroin, i´ve never got "high" again. I was using it just to feel the same way as i do now, drug free.
And this is easely explained. The recreational user has a very low habituation threshold.His body is not acostummed to the drug, and thus his body reacts in many diferent ways. While the regular user, has his body acostumed to the substance, and it doesn´t affect him nearly as much.
It´s like a no drinker competing with an alcoholic so see who drinks who under the table. The alcoholic will always win, because his body is acostumed to drinking. It is very, very hard to get a serious alcoholic man drunk. He will drink all night long, and you won´t see him waver. It takes massive ammounts of the substance to get him into the same state as a recreational drinker would after a couple of whiskey shots. It´s the same with hard addictive drugs.

Another urban myth:
It was heroine, cocaine and pills. Main drug was heroine.
And no, it´s not that simple. For example, back then when i started doing hard drugs, there weren´t any "role models" to compare with. No one knew what the long term useage of the drug would do to you. No one had ever seen a "junky", no one knew what an "overdose" was, no one knew what "spiked shit" was and that it could kill you. If back then i knew half of what i know now, i would never have tried the shit. What happened to us back then with heroin, is hapening now with Exctasy. Young guys are taking them like Smarties, not knowing what it will do to them on the long run.
Everybody needs an outlet, a form of escape, a vent. Some use alcohol, some use food, some use extreme sports, some use controlled substances, some use tobacco, some use Valliums and that sort of thing, some use gambling and some don´t use anything at all and keep all the frustrations and hardships bottled up, untill they eventually explode into a violent rampage and go "postal".
The stress of life and routine in our day in age is what drives most of us to search for an outlet. The only reason why hard drugs are not so wide spread is because its illegal. If drugs became legal, we would see an explosion in comsumption the likes we´ve never seen before.

In my view, alcohol, tobacco, heroine, weed, and any other substance that creates a physical or psychological addiction should be rated exactlly the same. They should ALL be legalized, or they should ALL be banned. Having two measures or double standards is highly prejudicial and hipocritical. Why should the alcoholic be excused and the drug addict be condemned?

And finally, regarding criminal behaviour:
Criminal behaviours are to be condemned, wether the perp is high on drugs, drunk, or sobre as a nun.It is not the man´s condition that deserves punishment, it´s his actions.
If a drunken driver runs over and kills a mother and child, he should be jailed. Just as any other driver should. Wether he was under the influence of something or not, should not be basis for excusal or condemnation. Only the act itself can be judged, not the person.

*Did i spell "sobre" right? Will anyone please tell me how, if i didn´t?

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"Quincitilius Varus, give me back my legions!"
Emperor Augustus of Rome.