To hear something, to understand something, does not connect in a human brain to logical action. It does not lead to belief.
It is why, despite facing the death penalty, people still commit murder every day in the USA.
We actually encourage our fellow humans that belief is more important than realism or pragmatism, in so many walks of life. It cannot come as a shock to then find that there are deniers out there.
The only issue is what we do about that. Slade's decision is much the same as a drunk driver. They knew they were going to get drunk, and yet they made the decision in advance to risk the lives of other people.
The only issue is where belief negatively impacts on other people. I have no problem with a person believing that God wants them to wear black and gold hooped socks, and if they don't they will go to what for them is Hell. Because it has no impact on me at all. I can still think they are daft, but, whatever, if it makes the world go round and keeps them happy.
I really don't care if Slade catches Covid, ends up in hospital, and suffers life changing side effects. That's his problem. I baulk a little that it might then impact on the taxpayer, but money is only a construct anyway.
That, in some minor way being hospitalised might deny someone else of treatment, might irk me, but we all make similar decisions every day about diet, smoking etc. So I am down with that.
But, if he catches Covid and, not being 'protected' by a vaccine, is more likely to spread it, and as a results gives it to someone else and it negatively impacts on them, maybe kills them, that is where the line gets drawn. Sure, the chances are slim, just in the same way as thousands of people drive impaired without killing anybody else every day, but, for every person taking that decision not to get vaccinated, increases the chances of someone dying as a consequence. Not cool, not cool at all.