Any nation developing nuclear weapons is a threat. I could very well believe that Iran's nuclear program has peaceful intentions if it were not for the fact that they had been hiding it for so many years and are still being incredibly secretive about it. A nuclear program intended purely for peaceful uses has no need for secrecy. The only purpose of concealment is to protect military applications. Of course, this in itself does not prove that the program is military in nature, but the rest of the world can only safely assume that it is, and act, before any potential for weaponization is realized. If Iran were to just open itself up to oversight from the international community, we could settle the issue today.