The cosmologist Carl Sagan popularized the notion that "extraordinary claims require extraordinary evidence." Yet when it comes to Iran, it appears the rules of evidentiary common sense are out the window.
Exhibit A (via Larison) is a recent speech by House Majority Leader Eric Cantor in which he claimed that: "If given the opportunity, Iran's leaders would make good on their call to wipe Israel off the map, and armed with nuclear weapons would be a threat to all within range of their missiles, which someday soon may include our own shores."
What Cantor is clearly implying is that once Iran obtains a nuclear weapon (if they do decide to build one) they will use it to wage a suicidal attack against Israel. This is an extraordinary claim, given that no nuclear state has launched an unprovoked nuclear strike against another country no matter how bitter the rivalry. Of course, it's possible that Iran's leaders may decide to do something that's clearly insane, but the weight of historical evidence against this claim is enormous and self-evident. Pakistan has not nuked India (or vice-versa). The U.S. and Soviet Union avoided nuclear war, despite some harrowingly close calls. States that obtain nuclear weapons, with the single exception of the United States during World War II, do not use them.
If Cantor believes Iran will break this pattern, he needs to back it up with serious evidence, not a wave of the hand.