My thoughts:
1) The game will be better to the extent that we all show some minimal degree of consideration for our fellow players. I suppose this could include language, to some degree. I have learned the hard way that there is a large portion of our society who react strongly to swearing, and that it is often practical to be considerate of this preference.
2) However, I have not observed that language, including cursing, is anything other than symbolic. The real quality of a person is independent of whether they swear. The underlying emotions and willingness to pursue different options are there regardless, and largely independent of external indicators. There are good people who swear from time to time (like me!!), and there are bad people who never do.
3) Look at these boards. Swearing is generally prohibited. However about 1/4 of all posts I have read consist of someone trying to hurt someone else verbally. Are the motivations and actions of these people any more justifiable because they don't swear? No.
3) I believe that a parent should prepare their kid for the fact that language is just an indicator. Trying to totally shield them from swearing, and other more substantive aspects of human communication, is futile. They will encounter it eventually. Better to explain it to them. That so-and-so is swearing. This indicates such-and-such state of mind, which would be there whether he/she was swearing or not. They may be angry or excited. It may be a social bonding mechanism used with their on-line friends. It does not indicate that they are evil or bad persons (although it may show a certain lack of consideration, depending on what forum the swearing is occuring in, and depending on whether they have been asked to tone it down and refused).