I'm going to start with the most basic of arguments for this. The fact of the matter is, this is a bloody, gory game, and it seems totally backwards and bizarre to get mad at people for swearing in a game when the objective of said game is to liquefy your enemies in to dripping, messy piles splattered among the walls.
This game is rated Mature for a reason. You should be one of two things if you are playing TF2: A 17+ adult (or near adult if you're 17) or someone who is younger than 17, and among the potentially "harmed" by foul language who bought the aforementioned described game. If you are the former, congratulations! If you are playing this game, you have undoubtedly heard every single curse word our wonderful language can offer. If you are the latter, then that means one of two things. You are a delinquent or your parents don't care about the game's gratuitous violence. If you are the former. Congratulations! You have undoubtedly heard every curse word our wonderful language has to offer, and have likely used them as well. If you are the latter, then its apparent that if the parents are uncaring of violence, let alone swearing. I have created a simple flowchart that illustrates my previous points.
If for some reason this does not convince the administrators to lift this rather unusual policy, perhaps we can compromise, and lift the policy at late server hours when it is very likely only adults are playing. If a young player is up late, chances are they don't care about language either.
Let's make this happen people.