Breaking promises with them means we give up the ability to work with them diplomatically on other goals. "They haven't done everything we'd like them to do" isn't a valid response to someone fulfilling the terms of an agreement you've made with them.

Trump chose to break promises. Now we are seeing the outcome of the resulting breakdown of diplomatic relations.

This is the kind of politics that's hard to say which position is the more optimistic or jaded. Or both at once.

At some point we have to try to make things better, and believe that better (even just a smidge at a time, and possibly with great effort) is possible. Or else we might as well just build the suicide booths from Futurama.

It feels deeply cynical and jaded to me to say, well, just let Iran fund armies and encourage ethnic cleansing, as long as they don't do this one specific thing that is more important to Americans. As long as the horrors you create only affect people in the middle east, we can look the other way.

I'd say the cynical position is the one that says "we can't improve everything all at once, so let's not seek incremental improvements."

In the Obama deal Iran was allowed to back out if the US broke its terms of the agreement (which happened because of Trump pulling out), so they are acting 100% in accordance still with the original Obama deal. Do you have evidence otherwise?