I can understand your frustration and confusion. When I was a freshman, I went through recruitment in the fall, and it was true that some of the PNMs were not as nice as I expected them to be. What you should take into consideration is that maybe these girls are acting this way b/c they feel insecure in their new surroundings, and started "talking trash" to make themselves feel a little better. (Or maybe they are just not nice
).
The point is that if you feel comfortable around the greeks and wish to know what rush is like, then go for it. As far as my school is concerned, you don't have to accept a bid or join a sorority just b/c you attended a rush event.
Also, sorority can change the way someone behaves (and all for the good I can tell you). I know that I would never want someone who disrespects other people for their differences as my sister, b/c she could easily say those things about me. Just go with your gut instinct, and it won't matter if you join or not, I am sure the sisters will respect your decision either way.