Well, most heavily multiplayer based games cater to a much younger audience. Hence why most of them have a terrible community due to immaturity which completely ruins the online experience (battlefield 2, runescape, halflife, and unreal tournament to name a few). However, i do find that multiplayer games that require a monthly fee to have a much more mature communty. I was just shocked when i played Eve Online and on my second day an admin came up to me in the game, welcomed me, showed me around, and helped me figure out what to do!
Another factor that causes the community to degrade to a boiling ces pool hate and flaming is when the game requires large amounts of skill on the players' part. People often feel the need to defend their pride, and thus the words "pwned" and "n00b" were created for that purpose... So, let me just restate the reasons i think M&B should remain SP (or if it were MP, it should be co-op ONLY). 1. It requires large amounts of personal player skill. 2. No monthly fee 3. Games would be hosted and moderated by the players (most likely). Which all mean that the game, and the communty would deteriorate beyond recognition. I could easily see these forums resembling those of runescape or blizzard within a few short months after the MP release.
Also, i'd like to add that IMO SP games are just far more memorable. Again, IMO most of the MP games are actually "fads". Good SP games never really get old, are unique, can never really be replaced, and you'll almost always come back to them after a while. MP games on the other hand are largely just "upgrades" of older versions. New one comes out, and the old one is now obsolete and has nothing to offer. People went ape **** over bond for N64, then perfect dark came out and bond was soon forgotten, then came halo(cheap ripoff of UT) which saw the end of all else...etc etc. Same goes for most MP pc games as well. Sorry for making this such a long post, just had alot of opinions to share.