I think that the con team relied too heavily on examples and appeals to emotions which really did not provide enough support for their claim that the stand-your-ground law is not effective.
"Guns don't kill people; people kill people." I think this is a compelling argument. The problem may not necessarily be the guns/gun laws but the people. Violence will still exist, guns will still be used regardless of the amount of restrictions on gun ownership. But then again...guns enable people to kill people. So while it's a good argument, it does not fully support the stand-your-ground law in and of itself.
The con's argument that self-defense is too subjective, especially without witnesses, was one of the strongest of the debate. It relates directly to the Trayvon Martin case because there were no witnesses before the shooting, and this is exactly what the controversy is over.
I think that the pro's argument that everyone is safer with more guns on the streets is significantly flawed. The logic isn't there or it wasn't explained right. If there would have been better statistics to back this up, possibly the amount of deaths by guns relative to a state's gun restrictions...The Canada/UK burglary statistic was helpful, but I'm not convinced that the reason the US burglary rate is lower is because there are more guns; it's a correlation, not causation perhaps.
Overall, I think the con team won because of their focus on the subjective-ness of the stand-your-ground law.