I suspect the main difference would be that alcohol is only really harmful if consumed in large quantities: Plenty of people consume small quantities of it and get pleasure from that without causing any noticeable harm. Ditto fatty or sugary food - and there you also have the issue that I believe a small amount of some types of fat is now considered important for health (even though an excessive amount is detrimental). On the other hand for cigarettes, any amount is harmful.
But realistically, no-one to my knowledge is remotely proposing that we ban alcohol or fatty or sugary food, so that seems to me like a strawman argument. Almost all political decisions come down to a judgement call about whether the good of doing X outweighs the harm of doing X: That's inevitable because pretty much every political decision will have some unintended bad side effects. If people think the balance goes one way for one thing (smoking), that doesn't mean they are going to make the same decision for other completely different things.
Indeed.
Also, I suspect that given there's many way around it, the ban on sales of cigarettes based on age isn't likely to actually impact all that many people.
Plenty of people manage to buy things which aren't all that readily available. Yes there's an added cost (for example travel costs,. shipping costs, etc.) however for those who wish to do it they will afford that costs.
For those for whom it is now a significant barrier to easy access (for example older kids buying cigarettes and selling them at £1 a go when they've paid far less than £40 for a pack of 40 to those under age in the school playground isn't likely to happen as widely, given those under age can't just wait, say, 10 months until they can buy them legally) there's a good chance there'll not bother with the effort of starting.
Whilst there's likely to be more restrictions brought in as time passes, it's going to be something which impacts on a smaller and smaller number of people, so fewer people will be overly bothered by those changes.
Having said that, it does appear the story of thing which isn't necessarily that helpful in reducing the numbers smoking (in that a lot fewer people do it then before - and as a percentage of the population is reduced further) so why go to the effort of making significant changes.
Bring in rules limiting the number of places you could buy or marginally increase the age to 18 or 21 (over time) could bring about a lot of the benefits without being so controversial.