I agree that this would be a great feature with the appropriate abuse-preventative measures in place but I also believe that leaving another party that needed a tank just because it wasn't your friend's group is indeed poor form. I mean, I completely get that it's a sigh-inducing and frustrating situation when it happens but that's the risk you should be willing to take when you know full well that you may not get into the specific run you were looking for. Those people needed help too but instead it seems like you choose to slap them in the face just because "Oh I don't know you, so I don't care".