I've never understood that (well I do, money) why they keep fags n alcohol yet frown upon illicit drugs. Fags are known to cause lung cancer and well we know about booze; violence etc, etc, etc - in my view alcohol is one of the worst drugs (she says, drinking stella cider, spelt cidre) yet it's legal and other drugs that are less harmful are ILLEGAL.
Tobacco probably avoided banning as it's use was
so widespread it'd be a great way to lose an election to try and take it away from people. Plus there's not only the tax but also British owned tobacco companies that can pay to have the law suit them cos half the politician are probably also 'consultants' on the board of 'em. That and they lied through their teeth for years and buried the evidence proving the link with lung cancer for decades. Booze would be much the same story. Snouts in the trough and a guaranteed election-loser to even suggest a ban on it.
The more conspiratorially-minded may also point out that tobacco does nothing to prevent a person from doing their duty earning the money to spend on fags and booze that ends up in the pockets of those who make the laws (and/or their school chums and relatives and that). When it does prevent them from working then you can blame them for being a drain on the state for being so stupid as smoking tobacco and it's a handy excuse to bump the taxes up and up on baccy and pretend it'll be spent on the NHS treatment they now need for the rest of their lives. All pays for itself and is a nice lil earner for drug dealers in suits.
They may also point out that alcohol depresses and numbs people which is just what you need to convince somebody to slog their guts out doing a job they hate to earn money to spend on fags and booze and so forth. Much the same again only has the added bonus of increasing crime (especially violent crime and mindless vandalism and the like) which means you have a handy excuse to keep raising the taxes on it to fund more police to spend their time arresting drunks. Create a problem then arrange it so it appears you're trying to solve it but really you're just going round and round in circles. And keeping the booze lobby happy. And profiting - directly or indirectly - from it too, Plus now you have fuckloads of police in case people get all worked up about illegal wars or poll taxes or whatever happens to be the thing you're wanting to inflict on those people who you'd rather weren't too close but glad there's plenty of 'em and most at least semi-addicted to booze and/or fags cos it does work out quite handy one way and another.
Other drugs became illegal for various reasons. Most of the 'street' drugs were banned worldwide cos America said so cos they didn't like the way that those ghastly ethnic types preferred to smoke a bit of weed that grew wild and didn't bring in any taxes, or they liked to smoke opium to escape from the brutal reality of being considered little better (actually usually worse) than animals who you could get to do really the really hard, really shitty jobs for next to no wages, or those folks who sniffed a bit of cocaine cos they actually were more or less still slaves and cocaine was cheap and legal and meant you could get through the day.
And as for psychedelics... those fellas really do scare the people who generally make laws. Look what happened when they became prevalent? People started protesting against wars and racism and sexism and homophobia and generally started to spot that life doesn't have to be as crappy as it often is. They cause people to have ideas. Often bloody stupid ideas for sure, not always so stupid though and that's a risk too far.
I'd probably best leave it there but you get the idea.