I think the point is that if you're unvaxxed, everyone is potentially a threat, whether they are vaccinated or not. While I can make an argument that on an aggregate basis the vaccinated likely have a lower chance of transmission, on an individual basis the outcome is binary--you either get COVID or you don't. And if you're unvaccinated, getting COVID is a potentially dangerous or deadly outcome, regardless of age or prior health (although those factor in). So for the unvaccinated, you should view every person around as a threat. You shouldn't feel "safe" just because you're around vaccinated people.
That, of course, is an even stronger argument for getting vaxxed, IF you're taking precautions and you are worried about COVID. If you're going to mask and be socially distanced because you're not vaccinated, then you're forgoing certain aspects of life you might enjoy, such as meeting your friends at a pub for beers, because you can't actually consider ANYONE to not be a threat. COVID may not go away for many months, or years, or ever. So not getting vaccinated means that you're rolling those dice every time you ever go around other people.
Of course, there are people who choose not to get vaccinated, won't wear a mask, and have no intention of social distancing, and are not worried about COVID. Those people are already rolling the dice, knowingly, and taking the risk that if they get COVID they'll be fine. The good news is that for most of them, it'll work out just fine. Those few who it doesn't? Well, those are the ones in the hospital, ICU, or morgue right now...
