Some of the comments regarding "Stupid girls" are well, not wrong. Arisa never did seem like the brightest bulb of the bunch and does seem like the type to be easily deceived. Like an idiot who sees something and believes it on first sight without doing due diligence. As for the rest of the group, the plausible explanations for this is herd/group/factional mentality and the unconditional trust they have for Arisa.
It's also very important to observe that Amane, Sofia, and Shiori have demonstrated above average intelligence and are not a part of the clique we see - Arisa and the original girls are all part of the same clique. While the crafts-girls aren't socially bright nor considerate of circumstances.
I'm pretty sure most people have experienced similar or observed IRL some real stupid things when people act as a group ("sheeps" as some are called). By that I mean those people in the group will literally continue to double, triple (and so on...) down on their own mental/social mistake and believe themselves to be right until things go wrong physically. See the hyperbole on US farmers and the current POTUS policies.
In other words, some people can only learn by FAFO. But I think this manga won't go down that route, I think, I hope...? MC does seem to have more tolerance for it. I have seen too many stupid things now that I can't dismiss anything. Stupidity is beyond infinity after all.