I think it should never have been legal in the first place (as it is, it's addictive, common-place and considered socially cool by a lot of teenagers, so before they are responsible enough to make life-changing decisions they go and get themselves addicted to a substance that is detrimental to your health, your social life and your wallet). However, given how much opposition it would face, I don't think it should be made illegal, the financial and political backlash would be immense. But the fact is, it is like crack or cocaine in slow motion; you get addicted, it messes with your organs, it costs you shit-tonnes of money, but it just takes a lot longer than other drugs, however, because it's legal a lot of people get addicted because those who put peer pressure on them to smoke have such easy access to it.
I propose a middle ground, heavily tax it, meaning it will be less accessible, the health industry gets an added boost to its income, it won't sell as well, less people become addicted, people looking to quit are given a 'nudge in the right direction' and it becomes less ingrained in our society, meaning we won't have to make it illegal and therefore impose upon rights, because the increased price will push the entire smoking industry to kill itself.