If you study recent history you'll see Iran has not invaded neighbouring countries or launched pre-emptive wars, which cannot be said for the US, Iraq under Saddam or Israel. If you look at Iran's strategic world view from the Tehran perspective you would see a country that views itself as surrounded by potentially hostile forces on many fronts: Afgrhanistan/Central Asia has US/UK troops and bases, so does Iraq, the GCC states were organised as such as an anti Iranian defensive alliance, the 5th Fleet's in the Gulf, many Pakistani Sunni clerics see Shia as heretics deserving death (Pakistan IS nuclear)... then there's nuclear Israel which has shown the ability and will to project power well beyond its borders: eg. Osirak and Tunis. For Iran a nuclear deterrent makes sense. The Iranian bomb, if one comes, is not for use against you Israelis. Iran would get pulverised in response and knows it. Besides turning Israel into a nuclear desert wouldn't exactly help the Palestinian cause.
Palestinians report IDF airstrikes on Islamic Jihad targets in southern Gaza Strip (Haaretz)
from the article: Will Bush make Iran the only superpower?