I have witnessed many things in my time playing Team Fortress 2. I have seen people burn to death because a Heavy wouldn't drop his sandvich, because a Sniper wouldn't throw his Jarate. I have watched people call MEDIC over and over, while said medic simply fires his crossbow into a crowd. I have seen things that would make even the seasoned veteran cringe. I have seen this game go from Team Fortress 2 to Hey-how-many-points-did-I-get-this-round-what-we-lost-really-I-didn't-notice-Fortress-2, or HHMPDIGTRWWLRIDNF2.

Scouts: Mad Milk can put out teammates too.
Soldiers: You have three different battle banners, all of which can provide aid at a critical juncture. You can whip those teammates into shape with the Disciplinary Action.
Pyros: You can airblast everything away from teammates, even spies. You can use the Homewrecker to save that Sentry.
Demoman: You can push the cart even faster with the Pain Train, and the Stickybomb Launcher is a good teamwork weapon.
Heavy: Those sandwiches aren't just for you. Feed a hungry teammate, save a life. And if you have a Medic kind enough to keep you alive, try to return the favor. Block those rockets.
Engineer: Dispensers and Teleporters can help just as much as sentries can. Use them.
Medic: You are THE team player. Use that Medigun wisely. And those
Sniper: You can do more than headshot. Jarate can put out teammates, and give others a chance to kill that Heavy. Throw it at spies approaching teammates too.
Spies: Sap everything. Backstab those most in danger of killing your teammates first.

So I call on you, the Team Players. Fight. Not for the high scores, not for the glory, but for victory. For those who need it more than you do.