I completely agree with you, OP, and certain other PPs, but unfortunately, COVID and the rationality/proportionality of responses to it have become one of those things that you're just not allowed to question - at least not without being called all of the insults under the Sun and branded a granny-murderer.
As I thought you made very clear (but many seemed to believe differently), it is not technically compulsory, but if you are not allowed to live any kind of normal basic life without it, it effectively does become compulsory.
I'd say it's along the same lines as there being no UK law that forces you to have a bank account - but just try living any kind of normal life without one. Accessing the internet is quickly heading that way, too; the great many elderly folk (and others) who do not trust or understand it and/or have no interest in it or confidence in learning to get online are currently able to live a vastly inferiorly-served life without it, but I don't think it's going to be long before any vestige of choice is effectively removed, along with the assurance that a 95yo bedbound person can easily toddle along to the library and access it there, thus 'nobody is excluded'.
In fact, we're seeing a similar thing with the masks now. There are people who have genuine medical reasons not to have to wear them (some of them simply cannot breathe with one on), but although they are legally exempt, we all know exactly what response they are receiving in reality if they dare to go out in public and try to buy food or access other essential services. It's basically a form of democratically-endorsed discrimination and hatred against the disabled.
If this were like The Plague where almost everybody who contracted it would soon die a painful death, I'd understand the reaction far more; but it's a virus which has no or minor effects on virtually everybody who gets it.
I will get abused for this view, but I also think the total official number of deaths is legitimately questionable and fundamentally flawed, when anybody who tests positive (or, in the early days, was assumed to be, based on often-generic symptoms) and dies of ANY cause within four weeks is counted as a COVID death. The most vulnerable to COVID are also virtually all those who are already most vulnerable of dying from old age and/or existing health conditions. Over 1,800 people die in the UK every year from road accidents and doubtless all of those will have drunk water in the week before they tragically die - but nobody in their right mind would ever dream of attributing their deaths to 'consumption of assumed-poisoned water'. Of course, I accept that COVID or any kind of virus will sometimes ultimately be the reason for (or a major contributing factor to) the death of a vulnerable person, but there are no guarantees whatsoever that it is undeniable fact in every single case. Indeed, for all we know, a young, fit person could contract COVID and then fall off a sheer cliff on to jagged rocks below, a fortnight later and, going on the stated statistical criteria, be subsequently accounted for as a COVID death.
I also think it's very interesting that it's being hailed as the perfect fail-safe solution to protecting the population from a 99.5%+ non-serious virus by rushing out now to administer a vaccine that has, so far, been declared to be anything between 70-95% effective.
The comparisons with things like seat belts and airport security measures are crazy. A seat belt is external and does not have a continuing effect once removed. I'm happy to accept that I cannot travel abroad on a plane , should I refuse to comply with the regulations; indeed, have long been denied the right to go abroad at all should I refuse to obtain and pay for a passport. What I can't accept is that I potentially could not even buy food anywhere in my own neighbourhood unless I agree to have chemicals and organisms irreversibly inserted into my body, regardless of what those ingredients may or may not be; and if I DO 'agree' to it (the alternative being basically an inability to survive), what step comes next 'for the safety of everybody' - ensuring that I don't hold any non-government-sanctioned views or beliefs which would thus define me as a 'potential terrorist' and similarly see me banned from shops or any other public places unless I renounce them? It's about fundamental personal liberty - and promising to ensure somebody's freedom under virtually impossible conditions is no real liberty at all.
I await a flaming.