Even if they're not vaccinated. Yes, it's a serious illness. But if I meet another young healthy person who acts like it's guaranteed to kill them, I think I may weep. There are young adults in their 20s and 30s cowering at home in complete disproportion to the risk. There are a few in my extended social circle who refuse to go outside at all, even one who is fully vaccinated.
But it's like my own GP commented at one point during this. You're still far more likely to die of a heart attack. I'm pretty sure that on average, a year of heavy stress, social isolation, junk food, booze and TV for a young person is certain to knock more years off their life than COVID-19 would. Personally, I've been going for daily runs in my low-density suburban area throughout this all. Some have reacted to this like it means I'm suicidal, but even if the estimates on outdoor transmission are like 10x too low, it's still likely the better choice for my long-term health.