That is why I am always nice by default. Because I cant just judge each individual before I see if they are good or bad. And in the majority of cases it takes days before I notice that a bad person is actually bad, and until that point I am still nice to them.
Most people judge by first impression for some stupid reason, I judge by observing how they interact with others (or me), which takes quite a while to do.
While I do not count Membership in most Groups as a thing to judge Individuals by, I sadly see it very often how those Groups act on a larger scale, which is my actual gripe with them.