But pubs do make a much larger margin on soft drinks than
they do on alcoholic drinks.

Christian McArdle:
I think it is justifiable, though. You can't drink many pints of Coke in the
same way you can with beer. I bet that statistically, a soft drinker will
spend a lot longer in the pub for one drink that the average beer drinker.
Therefore, soft drinks need to have a larger mark up to get a fairer share
of the fixed costs.

I totally agree. In fact, whereever there's a free market, such as the
examples above, I believe that any pricing is fair and justifiable
pricing. Smart retailers know that profiteering is only good for the
short term.