Up in LEM, Supreme and Global ranks, I've actually had a really nice handful or two of games where the people in the match definitely were not American, and everybody got along, without question. I guess the actions of the people on your team vary upon how serious they are on the game, and in a way on how skilled they are. (Generally, the higher the rank, the more serious people get. Not to mention, you can't exactly smurf in a supreme match, so you don't get THOSE starfishs.) That's not to say that you need to get pro in order to get good teammates, but that the community gets worse the lower ranked you go most often. It's harder to find a pair of people not trying to smurf, throw the game, are actually starfishs, etc. in higher ranks because as I've said, people take it serious.
I'd say the community gets better the higher ranked you end up on Competitive, but there are a few bad apples who chuck all their forgets out the window and decide to le epic troll xddd without a complete 5-man.