I am going to respond to several messages at once. I think the R&R vs. C&M animosity is based on a few factors:
1. Notes from the production staff indicated that they broke up R&R specifically to make room for C&M, and that the writing staff does not want more than one couple at a time. R&R had a very profound affect on many of us that C&M did not have, especially after they made the horrid mistake of making Monica a terrible shrew for almost a year. I understand that this has been rectified. There seems to be an underlying understanding that only one couple is going to be an ongoing concern, and C&M have basically won. They had, as of my last viewing, (which was months ago) begun to overpower the show with dull, limp, predictable plots. R&R as a couple never dominated the show as completely, or for as long, and C&M did. The other problem is that C&M also made the wonderful C&J storylines much more rare.
Since I've now come to the conclusion that Rachel is a vacuous little twit who can't love anybody properly anyway, Ross is well rid of her and Phoebe may indeed be the more interesting pairing for him. If Rachel hooks up with Joey, we'll get to see two pretty, very shallow and empty vessel hook up and that might be fitting. I really want to see Rachel die alone, though. :-) (I love to hate her. Aniston is extremely gifted.) Actually, my ideal ending would be for a desperate Rachel, her biological clock ticking, to make advances on Ross just as he rediscovers Julie, rejects Princess Bitch, and heads finally into the sunset with his one true love.
As for it being a given that R&R will never get together again... uh, no, that's by no means a given. The writers remind us of the possibility a couple of times every season. Even by the time I had to stop watching this year they had thrown in the reminder TWICE. (R&R's kiss in the first episode; a comment by Rachel that she might marry Ross in a later episode. And remember; they *are* each other's backups. That may or may not be remembered by the writers.) Any statement like that from partisans on either side is just that - a partisan jab based on wishful thinking. It is a given now that C&M will marry, but it is not a given that C&M will stay together, or that they will get divorced, or that Chandler won't discover that he's gay, or anything like that. The writers will do whatever whim comes to mind, whether it actually makes sense and is good for the show or not, and the ratings battle ahead will have them pulling outrageous stunts.