I agree with your sentiment about civility. Too much has been lost in the internet age. Looking at how the shows were ended, however, is a different story entirely.
IMO, Lost and NuBSG both suffered from an odd writing style and a certain level of mismanagement. They tried to cram too many cool/spiritual/philosophical/whiz bang things for them to live up to their own hype in the end. The show-runners alone were responsible for the expectations they set during the course of their shows and I don't think it's terribly unreasonable for the fans to expect a higher standard of an ending to match the bar set for the rest of the show. Sopranos went even farther and treated us all to a non-ending after years of major hiatuses and half-seasons - the very height of pretentiousness. Hell, at least Lost and NuBSG made an attempt to have some kind of closure, no matter how meager. Sopranos never even tried - if ever there was reason to threaten bodily harm to a show runner, that would have been it! I jest, of course, but still, don't cock-tease your fanbase throughout many years of set-up and loyal following, only to walk out without the happy ending (or any ending at all)! Some people will always react viscerally to something they feel like they have a vested interest in, particularly if they feel like they were kicked in the nuts like some of the fore-mentioned shows. What they don't realize, is that not every ending can be a M*A*S*H "Goodbye, Farewell and Amen" or TNG "All Good Things".