The article's conclusions depend entirely on the definition of harm and seems to ignore the particular group's perception of it.

For example one citation used in support of the conclusion is conservative's opposition to getting the COVID vaccine. That group perceived harm in getting the vaccine (whether right or wrong). The article claims the group opposed the vaccine merely as a reaction to the vaccine push from outside the group.

So maybe the conclusion would be stronger if stated as "groups have a hard time making rational calculations of harm when facing a perceived threat from an outside group".

Doesn't really change it too much, but it seems quite unsupported in its assumption that these groups actually perceived themselves to be harming themselves.