All of the opponents to the Iran deal are confused and delusional.
Is Iran a dangerous state and not to be trusted? Yes. But they are trustworthy on some things. They are, in fact, our allies in the fight against ISIS. Without them, we could not keep ISIS in check.
Is it possible that Iran will use some of the funds released by the agreement to fund terrorism? Yes. But no one knows how much and it is already funding terrorism now. And our allies, the Saudis, also fund terrorism. 9/11 being the most glaring example. We do know that this agreement is something that will support the rising population of young Iranians who are looking towards the west for inspiration. This group can serve as a bulwark against the Iranian right wing and the Ayatollah.
Is the inspection process something that provides Iran with some ability to hide what they are doing? Possibly. But right now we have no inspection process and they can do whatever they want. With this agreement we have some way of monitoring what they are doing.
Will our not signing the agreement stop the deal? Nope. Other nations have signed on and will no longer punish the Iranians. So, Iran will be able to do whatever the opponents say they will do even if we do not sign. Is there a possible better deal out there that we can get if we persist? Possible, but not likely. This deal took years to make and faced opposition in our country and Iran. This is the best possible deal we can make at this moment.
How do we get Iran not to build nuclear weapons? If you know anything about selling, we have already won by getting them to sign the deal. What we all want is for Iran to join the fraternity of nations who abide by international law and decency (something the U.S. has not always done, btw). By getting them to say YES to this deal, this deal has created a situation where they will likely say yes to those larger goals. That is what salesmanship is all about.