Can't JR be described as "utterly obnoxious" for blaming the Barnes family or singularly, Pam or Cliff for everything negative in his life (otherwise his need for constant revenge was misguided)? Or wasn't Sue Ellen "utterly obnoxious" for blaming JR's cheating for her drinking and complete lack of independent thought?
The entire premise of the show...all the way back to Digger blaming Jock for every misfortune in his life, is based upon blaming the rival family. So I don't think it should come as a surprise that when the writers needed a reason for Pam to leave Bobby, they chose ...blame the Ewing's as the catalyst.
As has been said, Pam had no shortage of reasons for wanting away from Bobby's family but as we saw play out...when Pam left for good, there really wasn't a show left with any semblance of the original. It sucked...plain and simple. It was missing the thread that wove the two families together. The McKay's and Stevens were no replacement.