AI has developed this entire culture of people who are "into tech" but seem to not understand how a computer works in a meaningful way. At the very least you'd think they'd ask a chatbot if what they're doing is a bad idea!
I have a separate removable SSD I can boot from to work with Claude in a dedicated environment. It is nice being able to offload environment set up and what not to the agent. That environment has wifi credentials for an isolated LAN. I am much more permissive of Claude on that system. I even automatically allow it WebSearch, but not WebFetch (much larger injection surface). It still cannot do anything requiring sudo.
They are not. Many people are doing this; I don't think there's enough data to say "most," but there's at least anecdotal discussions of people buying Mac minis for the purpose. I know someone who's running it on a spare Mac mini (but it has Internet access and some credentials, so...).