It doesn't make any sense to say Iran should be left alone because estimates of their nuclear progress were overly pessimistic in the past.
These people are 7th-century, daughter-murdering morons with a history of lying as a matter of policy and as a staple of their religion, and we can't be sure what they're doing because they can't be trusted. The smart thing in the absence of perfect intelligence is to assume they are close to a bomb. You don't want to wait around until they nuke someone and then say, "Tulsi Gabbard was pretty sure this wouldn't happen."
They brought this on themselves by picking on Israel (unnecessary), killing hundreds of Americans, refusing to both abandon nukes and open themselves to inspection, and by continually threatening to destroy Israel and the US.
Imagine a world in which Islamists decided to leave Israel alone and let the Jews have their tiny sliver of desert. We could have that world this evening. The only barrier is Islamism.
Incidentally, Israel's success against its enemies is probably largely due to the fact that Muslim countries have expelled or killed nearly all their Jews. Where do you think Israel gets spies that pass for Iranians? From Iran.