My parents are refugees of the revolution too. I agree with everything you said.
The islamists hijacked the revolution. The risk is that the MEK or some other fringe group who is worse than the islamists hijacks the next one. A policy of regime change only works if you have someone internally who can lead an opposition. Otherwise, you are swapping one a-hole for another. All those people are dead or in jail in Iran. The failson of the shah is not going to survive long enough to consolidate power. The MEK is universally hated in Iran. The best thing the US could have done to effect regime change was to continue the deal. The people realized the islamist regime stole all of the money the US released. Before yesterday, the people blamed the regime for the problems, which helped to bolster the reformists who want the corruption out of the government. Slow secularization and democratization would result in a lasting friendly government. Overthrowing one bad regime to install another one won't. The hardliners are celebrating the end of the deal because it shows that they were right.
On withdrawing from the deal: This isn't some grand plan to get a better nuke deal in place. These are the first steps in setting up a pretext for the war that the neocons have been salivating over for decades. Right now, the EU is the only thing standing between this situation blowing up (forgive the pun) into a full scale shooting war. If the EU is forced to back out because of secondary sanctions, then Iran will start up its program again. Then Israel will conduct airstrikes in Iran with its new overfly rights granted by the Saudis (who might join in the fun) because Iran can't have a nuke (I actually agree with that position). The Iranians will strike back, and the US will be forced to act. I'm sure Bolton's power point presentation is a bit more detailed.
Any escalation in conflict, and especially the involvement in the US, will disenfranchise the entire population. The hardliners in government will solidify their position. The only way the US will get rid of them at that point is a full on ground invasion. Iran has mandatory conscription. So everyone in the country has some military training. This will be bloodier that Iraq.