Obama says: "Iran's development of a nuclear weapon I believe is unacceptable"?

If Iran is allowed to develop nuclear weapons. Then shortly after the terrorist factions will have them. And they will use them. That is why it is unacceptable. Why does Iran need nuclear weapons anyway?. If Iran were to be attacked by another country, the US would stand up for Iran and help defend their country for them. The USA are the police of the world and will not let someone beat up anyone else. Even if they do not agree with their form of government, or the leaders of the country.