If Iran is proven to have violated parts of the deal then isolating them now is an ideal tactic.
My bad, meant "stopping the export of terrorism" :) Appeasing them with useless agreements isn't helpful either. The U.S. is the only country who can really pressure them.
No intentions of exporting terrorism, hmmm? Didn't Trump didn't just call them the "world's leading state sponsor of terrorism" just two weeks ago? So have your cake, or eat it, but not both. As far as "offensive weapons" as you call it (the missile program, I'm guessing), My point is that by leaving the area, and dispensing with what influence we did have there, we're making it significantly easier for "bad actors" to aid Iran in that development. Those bad actors include, but are not limited to, Russia and North Korea. Neither have much cause to love us, both are undergoing a cash crunch and probably wouldn't mind making a buck while doing the US in the eye at the same time.
Iran has no intentions of scrapping offensive weapons or exporting terrorism. There is a large group of people in Iran who would like to overthrow the current regime. placating the current theocracy is not a good alternative.
Yeah, it's probably a good idea to alienate Iran and put sanctions on them so that they have nothing to lose by developing their missile and nuclear technology. By scrapping the deal we're throwing away one of the only effective levers we had to slow that type of program. We know that Russia, North Korea and China (amongst others) already have long range missile technology. By scrapping the deal we've created a US foreign policy vacuum there. I'm sure that other nations to who wish the US
ill will certainly understand our choice and be respectful of us not wanting Iran to have long range offensive capabilities. We have so many friends in the Middle East and, after all, the old expression goes "Nature really digs a vacuum", right?