Some great points being made by people here. I must admit I'm more of a single player or two player co-op man myself (it's what I grew up on in the C64 days) and rarely does a game make me venture from my cave into the wild world of online, so maybe I'm a bit naive and this is just symptomatic of the online community as a whole.
That said when Halo 3 first came out I never had any problems and often partnered up with people; now not a game goes by without me and my friends having to "avoid" players purely because they're jack-offs (for all the reasons people have listed prior).
That said when Halo 3 first came out I never had any problems and often partnered up with people; now not a game goes by without me and my friends having to "avoid" players purely because they're jack-offs (for all the reasons people have listed prior).