DaisyL, you say your plumber is a very nice man who 'believes that Covid is a government conspiracy'. We don't know exactly what he means by that - maybe he's not a 'Covid denier' or 'anti-vaccine' but someone who thinks that governments are using Covid as a means to control populations? Then the 10,000ish anti-lockdown protesters in London yesterday, most of whom also looked very nice ordinary, unmasked people, might agree with him.
I really don't know when it became acceptable practice to ridicule people who express a different opinion, or not the 'accepted' opinion. It happens all the time on the news channels to the extent that nothing they say is impartial. For example, years ago Prince Charles was ridiculed for being a 'tree hugger' and has since been proved to have a valid concerns about the environment.
Whatever the differences between your plumber and his wife, and she most probably would have a slightly different explanation, it's unlikely he deserved a tongue-lashing from Gransnet for being a conspiracy theorist. Also if you and he agreed that he didn't need to wear a mask then, it might be foolish, or wrong according to the government, but don't we always say 'your house, your rules'?