The previously mentioned offenders do not plug up the hospitals--and make the hospitals unavailable to the rest of us. I have a friend who has a kidney ailment--and her surgery has been suspended twice. She has a chronic pain. It could get critical if not treated. We can't blame the obese or speeders for her predicament.
And in some ways, we are already taxing the offenders. Speeders pay speeding tickets; smokers pay tobacco taxes.
I'm not sure the slippery slope argument will apply here. I can see this unvaccinated tax being lifted when COVID goes away.