Often in life we have to make decisions quickly about the people we meet. Consider a teacher in the first week of school, or consider coming into an emergency department at a hospital and having to decide whether or not to follow the doctor's recommendations.

The important thing is can we update our ideas about a person as new information comes along or do we stick to our first impression regardless?

And then, information gleaned in a first meeting is as important as information learned later on. It is extremely difficult to think of a reason for Darcy's statement about all the girls at the Meryton assembly, and his specific insult of Elizabeth, as anything but rude. I know people can be reserved in manner because of shyness, but those statements are clearly rude, and go beyond what can be explained by shyness or reserve. Darcy definitely has faults.

And, if someone like Bingley is friendly and at ease meeting strangers, they're probably not going to suddenly turn out to really be incompetents at the social whirl. Bingley is the sort of person I'd use when hosting a party to entertain shyer, less confident guests.