Offense and defense
Unlike football, for debate the best offense is not a good defense. The best and only offense is a good offense.
An offensive argument is a reason to vote for your side. A defensive argument is one that mitigates your opponent's case. For example, imagine the topic: the US should adopt an assault weapons ban. You are Con. An offensive argument would be that assault weapons empirically act as a crime deterrent, so banning assault weapons would increase crime. A defensive argument would be that past assault weapons bans have failed to significantly reduce crime. The former argument is a reason that an assault weapons ban is bad. The latter argument is merely a reason that an assault weapons is not as good as Pro might claim.
Voters should only be voting for offensive arguments. Defensive arguments, on their own, cannot logically form a basis for decision because they only mitigate the opponent's case. They don't provide an actual reason to vote for a particular side.
A good offensive argument has a link and an impact. A link is the explanation of how the argument relates to the resolution. An impact is the reason to vote for your side. Take, for example, the topic: Iran poses a greater threat to the United States than North Korea. You are Pro. You run an argument about Iran cutting off the Strait of Hormuz. The link is that Iran has the military capability to cut off all access to the Strait of Hormuz and has threatened to so in the past. The impact is that if Iran cut off the Strait of Hormuz, the US would lose access to Middle Eastern oil, which would cause a large uptick in oil prices.
In contrast, Con argues that North Korea might launch nuclear weapons at the United States. The link is that North Korea has operational nuclear weapons and has threatened to use them against the United States in the past. The impact is that a nuclear explosion in Los Angeles would kill 10 million Americans.
As the judge, you have to weigh Pro's Strait of Hormuz argument against Con's nuclear attack argument. For impact analysis, you are supposed to consider probability and magnitude. Probability is the likelihood that the impact will happen. Magnitude is the total size of the impact. A nuclear attack has a greater magnitude because 10 million lives is a much bigger impact than higher oil prices. However, given that the United States would retaliate against North Korea using nuclear weapons, North Korea would likely be deterred from launching a nuclear attack, so the probability of this impact is low. In contrast, Iran is far more likely to cut off the Strait of Hormuz given that the current Revolutionary Government has shown a willingness to resort to extreme tactics, such as when it took over the United States embassy in Iran. So the judge could still vote Pro, even though the magnitude of the impacts are smaller, because the probability of Iran harming the US by cutting off the Strait of Hormuz is much higher.
A good RFD should engage in impact analysis and consider both probability and magnitude.
If you cannot fit your RFD within the 1,000 character limit, say "RFD in comments," and leave your RFD in the comments section of the debate.
[A more extensive explanation of offense/defense and impact analysis can be found in post 4]