Return address

One of the arguments that I find unconvincing is that we don't need to worry about Iran having a nuclear weapon because they could never use it. If they did, we could retaliate since we would know where it came from. Call this the "return address" argument. It is often expanded to cover bombs that are delivered unconventionally since we would have a good idea where those came from too.

It seems to me that recent events undercut this line of argument. The people arguing that we need to engage Syria and Iran to shut down Hezbollah are tacitly, no, not even tacitly, admitting that those two nations are behind Hezbollah. They are, in effect, the "return address" of Hezbullah's Katushas. Since we are manifestly unwilling to hold the senders responsible in this case, presumeably out of fear of retaliation and Middle-East sentiments--it is not clear what grounds are there for confidence we would be willing to do so when the sender is armed with nuclear weapons.