]And again, it's because we are given so much information by the narrator that we accept that first impression, as do the people of Meryton, and continue reading.

I think this is it in a nutshell. JA has already set us up to think well of Jane and, Lizzy in particular, whose point of view we mainly relate to in the story. I think JA is leading us to do exactly as you say, come to the same conclusion as the people of Meryton. My first inclination, as already stated, was to feel the community rushed to think a bit too harshly. I had actually written this in my earlier post. I try not to make rash judgements on discourteous behavior up to a point on first meetings or on a single random meeting of people I already know because they might be having a bad day or something. Then I stopped to think it over and realized that Darcy's statement against Lizzy is the clincher: in my opinion, it is unnecessarily contemptuous, almost over the top when a simple, "I'm not interested in dancing" would have sufficed. Instead:

Your sisters are engaged and there is not another woman in the room, whom it would not be a punishment to me to stand up with and then coldly: She [Lizzy] is not handsome enough to tempt me and I am in no humor at present to give consequence to young ladies who have been slighted by other men.