Government isn't supposed to be a moral guardian for the country as a whole, the purpose of government is to organize and supply services etc to the population in such a manner as makes for a better quality of life for the majority of its citizens. On that basis, of course they should be supplying NHS, pharm grade heroin to addicts. The gains to society (in terms of a better life for its citizens) are many
Because the addicts are getting heroin that has to pass a quality control, there is much less chance of having people overdose because the strength varies
There are a LOT less crimes by addicts, such as burglary, to support their habits as they don't have to pay black market prices
Less money is channeled to organized crime and terrorism, both of which get substantial funds from involvement with drugs. This in turn will reduce their capacity to commit other (non-drug) crimes (org crime) or commit atrocities of the sort common to terrorism.
Far less money 'vanishes' from the economy due to drugs money leaving the country in return for the illegal drugs entering. This reduced balance of payments deficit produces more stability, less inflation etc (which is in the intrest of every citizen)
The users get what they want (making it illegal makes no difference to their desire to take the drug), other citizens get less acquisitive crime (by users to feed habit) and less crime associated with org crime because they have less money to do such. The same applies to terrorists and their crimes. The politicians even get a windfall because less disappears from the country's economy - all of the above are indesputably good for most citizens.
There still has to be some regulation; supply to minors should carry a prison sentance (obviously no decriminalization in prisons) or at least a removal of that persons right to have access to the drug; only fuckwit users would risk losing their supply for a few extra quid by selling to minors, but they'd deserve it. Additionally, any sales from an unlicenced seller should also carry loss/temp suspension of access to the drug. Very few would risk losing all by selling to an arsehole who'd lost their priviledges by doing something like selling to minors because the black market in it would be so much smaller.
As somebody pointed out, most users would then live fairly normal lives, and for the few that end up totally fucked out of their skull all day, every day on huge doses - at least they wouldn't be comitting crimes (they wouldn't dare risk losing their right to access if the had a fucking huge 5g a day habit).
The only losers in the above scenario are organized crime syndicates, terrorists and those sociopathic fuckwits who will not make the effort to conform to the current acceptable rules of society, regarless or not of whether they use drugs.
That CANNOT be any worse a working model than the one we have at the moment (prohibition); in fact it's a sight better for 99% of the population
