"Missiles that can fire north can also fire south." So felt a bunch of Latin American countries that joined the U.S. in resolving the Cuban missile crisis in 1962.
Missiles that can fire west can also fire east. This is the way China should feel about the prospect of Iranian nuclear missiles. In an uncharacteristic burst of short sightedness, they don't.
"The enemy of my enemy is my friend." That's the way China seems to feel in taking Iran's side in the nuclear weapons issue. For now, China and Iran have a common enemy, the U.S.
But the fact of the matter is, Iran is a lot closer to CHINA than to the United States. Meaning that the country will have missiles that can hit China LONG before it can develop missiles with a sufficient range to traverse the Mediterranean AND the Atlantic Ocean to threaten New York.
Right now, China wants to be Iran's "friend," because of the latter's oil. But China is a net CONSUMER of oil, just like the United States. Meaning that their longer term interests are closer to ours (a weak Iran) than Iran's.
Iran could easily become China's enemy someday. (It stands between China and its new interests in Africa, for instance.) If it were not for "ideology," it's the U.S. that should be Iran's friend, against China, for just this reason.
And Kublai Khan's "China" (Mongolians, actually), did try to, and succeeded in conquering modern day Iran in the 13th century, en route to the Mediterranean. Iran should fear the same about a country that overran large parts of India in 1962.
Some countries don't seem to know where their interests lie.