Pulling out of the Paris agreement and the WHO is definitely a negative - the Iran deal i'm not too fussed by. The Iranians aren't the angels they like to make out to be. They're actively supporting terrorist elements in Afghanistan, Pakistan, Yemen, Syria, Iraq, Lebanon and Palestine. They've got this shia cresent dream of a reign of influence and they're using militant groups allied to them to get it. Iran with access to modern weapons and a flourishing economy would only be emboldened to do more of the same.
I feel sorry for the people of Iran. If Trump had any sense he'd figure out a balance. Military sanctions, sanctions on government accounts and accounts associated with the leadership and Republican Guard - but open up to trade, tourism, education, research. Iran is full of bright people, they are isolated and deprived, it's driving them into the arms of the Ayatollahs. The regime doesn't reflect Iran.