The Iran deal was a step in the right direction but Iran is still shady about its nuclear practices and won't agree to a permanent stand down in the nuclear arena, it is still launching more missiles in violation. The deal was essentially a stopgap measure.
I don't want war but breaking the deal is a faster route to get there, the neocons essentially are planning that it fails so we can hit their sites/regime change (which is 1000 times harder with Iran than with Iraq). If we do rc in Iran, there are no more moderates and most of the previous moderates line up with the hardliners to defend Iran.
Honestly, stepped up sanctions explicitly over missile launches is probably smarter than tampering with the nuclear side