Here are MY thoughts on competitiveness
1) There is a relatively small percentage of people who take it too seriously, and who can make a match less fun for some people.
2) The vast majority want to win, and play fairly.
3) There is another small percentage who take league tennis less seriously than most. These people play for a different reason than most on their team. They may just want to get some exercise, or make new friends, and they don't really care about the match result. They feel that if they get along well with their opponent, that is a "win" for them. These people usually win less, because they don't really care about the result.
It may also depend somewhat on the level of play. At higher levels, people have been playing longer usually, and I see less bad behavior. It can still happen, but there are fewer players at the higher levels, and if you are a jerk to too many people, no one will want to play with you.