There are people on my F-list with whom I rarely, if ever, agree on certain subjects (politics and religion being RIGHT THE HELL UP THERE 99% of the time), and although I like these people for other reasons, I do in some sense choose to continue interacting with them for exactly the reason you mentioned. I'm a vehemently liberal girl who reads a ton of liberal blogs and, with the exception of my significant other, am surrounded by people who are equally vehemently liberal. While it leads to a certain degree of assumed understanding, it *also* leads to echo chamber, and I'd rather not be locked in to that kind of thing.