Ugh, the Holly episode, I absolutely agree that Blanche and Dorothy should have taken what Rose had to say into consideration - not one of my favourite episodes either.
I can understand why everyone hated when the girls turned on each other in some episodes - I thought it was realistic for the time though.
When Season 1 began, they were strangers having only lived together for just a year or two: Dorothy recently divorced and Rose, a recent and transplant from St. Olaf. By the time Sophia was in the picture, I never got a "we're close friends" vibe from them - heck they weren't even sure they wanted to live together after the grocery store trip but they made the most of it in the end. The reason I liked the first few seasons was because they were all still just "roommates" and getting to know each other - most of them didn't know each others' flaws and personalities that well and they came out in those arguments (Elliot, Gil Kessler, etc.).
In addition, the girls all came with emotional baggage (Dorothy trying to heal from her divorce, Rose not knowing how to be an independent woman after becoming a widow, Blanche relying only on looks to find love in all the wrong places, Sophia embracing and learning to trust new family in her old age) and they learned a lot more about themselves through each other than they ever did before they met. I don't think they truly began to start trusting each other and opening up until after Season 3 - the group therapy episode highlighted exactly why they wanted to stay together despite knowing how incompatible they are. I mean Blanche, didn't even feel comfortable selling portions of the house to the girls until Season 6 or 7 and you'd have thought by then she'd have done anything for them in a heartbeat but I'll chalk that up to a continuity error ;)
However, for all the crap they tolerated from each other -the evolution of their friendship over the course of what would be nearly a decade from "strangers who are just roommates" to "family" is truly rare and beautiful.
And for the sake of staying on topic, I can't watch the two-part finale, their final goodbyes are a tearjerker every time.