That question is actually leaning towards quite a bad argument, similar to a slippery-slope. Everyone has a threshold somewhere dividing acceptable and other activities. Someone having different standards for different substances is irrelevant. It is similar in character to someone saying a sin tax on sugar is the same as a sin tax on meat. Both in consequence, evidence of harm and in public acceptability those things are clearly different.
On this specific topic someone drinking sugar drinks is clearly less harmful than someone smoking, because sugar drinks have a strictly personal impact.
desiredState having or not having a different standard for tobacco doesn't cast a shadow on his opinions on sugar taxes.
An individual could sit placidly in the sun gazing out on a field of flowers and arguably be causing taxpayers harm because they aren't exercising and otherwise bettering their physical health (or maybe the pollen is increasing their risk of an expensive lung cancer, who knows).
There is more of an argument against taxpayer funds for the NHS than anything to do with sugar drinks in that observation. It is inescapably arbitrary what unhealthy behaviours are being subsidised vs. taxed.
That's because your observation is absurd and not grounded in reality. The reality is that obesity rates are too high in the UK. Most of these people overconsume sugary foods and overly processed foods. This in turn puts stress on the NHS, which affects all tax-payers in the UK so it's not a `strictly personal impact'. Overconsumption of sugar leads to measurably worse health outcomes than sitting in a field breathing pollen. The tax is not arbitrary.
It's a market-based solution to a market-based problem.
A classic problem which make markets inefficient is "externalities" -- the cost is artificially lowered because some of that cost is "externalized" away from the people selling the product. This artificially low cost causes the markets to allocate resources in a globally non-optimal manner.
One solution is flat regulation -- you can't have more than a certain amount of sugar in your drink. But that's unreasonable and unpopular.
Taxing is a market-based solution: it forces some of the external cost to be borne by the person selling it. This allows the market to allocate resources based on the actual cost, rather than the artificially low cost, while still maintaining the flexibility and diversity of the market, rather than having to impose regulation.