This is the same line of thinking people were peddling weeks ago when we arguing about the guidance not being clear enough "oh well I understand it so those who don't are thick." Ironically we're still arguing about it now given our government has performed a massive u turn on everything it told us all along.
Now it's, "well if people change their habits now they were going to anyway and they're selfish".
We know thick people exist and we know selfish people exist. Unfortunately those are the people most likely to spread the virus and harm the rest of us, so there's still a need for the government to acknowledge that and minimise the risk they pose to the rest of us.
If thick people exist then make the guidance understandable to thick people. Don't make it deliberately vague and then say "haha well you're thick if you don't understand it".
If behavioural scientists warn you that guidance had to be seen to be observed from the top down, or else you'll lose public buy in, then you observe it from the top down. You dont undermine it all just to protect one person.
Managing the virus involves managing people and their behaviour. That includes thick people and selfish people.