Contrast this to armed anarchists, anti-fascists, whatever, occupying city blocks as part of an organization that's connected to street violence and looting. The CHAZ guard, hasn't been trained and vetted and you don't know what his goals are and you haven't experienced it before.
As others have noted, it's a bit of a false premise to ask "Why are we scared of these people but not those other recent protests?" Because, of course, you assume people weren't scared by the other protests, which is not necessarily the case. Imagine someone who worked in one of the government buildings that the end-lockdown people occupied, there are now a hundred guys with masks and rifles occupying the building - is that imaginary worker scared or disturbed, and can you see why "But you aren't scared of the armed courthouse guards" isn't exactly equivalent?