First of all, I want to say that I hate people who destroy ladders on which are standing their teammates.
They are doing it and don't bear the consequences. Only in some cases someone makes a screen and then ladder-killer gets banned for few days.
After unbann time he usually does the same...
But, from the other hand, people (defenders - cause I'm talking about EU_2 & EU_5, where it usually takes place) who will destroy ladder with group of enemies on it, haven't got benefits from doing like that (excluding that the flag will stay safe for longer)
I don't know if here was topic like this one and I'm maybe recuring but my proposition is simple:
Make something like ladder-kills.
e.g.
Player X has destroyed a ladder with 3 of his teammates. They fell down and died. So player X gains -3 to his kill:death ratio.
or:
Player Y was a defender so he has destroyed ladder with 3 enemies on it. They fell down and died, too (yay, what a suprise). Player Y gains +3 to his ratio.
I would to know what are you thinking about it