OK, I've heard all the reasons why being able to hurt your team mates would ruin TF2, and I agree for the most part.

But here's a new take:
The person doing the firing, takes the damage. i.e, if you shoot and hit a teammate, the damage it would have done is incurred upon oneself, instead.

If a Pyro wants to Spycheck someone, they have to be willing to risk their own HP to do so. That way, they'll use more discretion when spychecking, and the rest of the team doesn't suffer. No risk of **** TKers, no problems with Heavies and Pyros mowing down their own team.

Thoughts?

PS. Yes, I play as Spy most often, and this is the main impotus for my post, but its not too much to ask is it? Esp considering the Pyro Pack's massive powerups...