I would argue that a tendency to not recognize the lack of merit in an idea is harmful in itself. Let us take your example of astrology. What harm is there in b

I would argue that a tendency to not recognize the lack of merit in an idea is harmful in itself. Let us take your example of astrology. What harm is there in believing it, despite no evidence nor any reason to suspect it is even a good hypothesis? For one, you might waste resources such as money and time reading about it, or getting readings. A minor thing perhaps. On the other hand, what about people who believe in it so deeply that they give away all their fortunes chasing nothing? What if someone ruins a relationship because they read in their horoscope that they should be wary of their partner? These are just a few example. I would also hypothesis that if one is willing to believe in one thing such as astrology, they are also likely believe in other things. Those other beliefs may also hold hidden dangers. Thus, it is important to always practice undiscriminating scepticism. Always try recognize what you don't know.