Iran's Islamic Revolutionary Guard has become one of the region's most powerful and dangerous military organizations, training and arming terrorist proxies in places like Lebanon, Yemen, Syria, Iraq and Afghanistan. Concessions are only going to embolden this radical organization and lead to further mayhem in the Middle East.
Any threat currently posed by Iran would be far worse should it obtain a nuclear weapon. Trump's withdrawal from the 2015 agreement only made that possibility more likely. These concessions are necessary in the interests of wider national security.
Placing the Revolutionary Guard on its terror blacklist was the first time in history that Washington designated part of a sovereign government as a terrorist organization. Reversing this is an essential step before Iran can return to any deal.