I don't think that the goal of international relations is just to stuff on 'the enemy' until the end of time. Iran's economy has been screwed up for decades because of Western sanctions, and the economic pressure finally forced their leadership to agree to a deal that amounts to a win-win for both parties. Iran doesn't want to be broke til the end of time, and the Western world doesn't want proliferation of nuclear arms.
Yes, Iran is a state-sponsor of terrorism and members of their government regularly burn flags and chant 'Death to America', but that can be constructively changed if the West keeps the deal up and Iran begins to participate in the global economy. Poverty and economic instability breed extremism, and it's likely that if the rest of the EU stay in the deal and Iran doesn't pull out, we'll see drastic changes in their society over the next 20 years as the country becomes more stable and wealthy - with assurance that they aren't going to develop nuclear arms.