Those proxies have been operating and formed long before Trump ever came along and sadly will be around long after he's gone...no government in the world can control or scare them. But they can intimidate them into action-such as Trump did...diplomacy would be the only way to deal with their leader-not intimidation.
The deal was for them to not be developing weapon grade Plutonium to avoid huge sanctions-now that deal is off the table, it's open season...once Iran gets to be nuclear capable...life will be sucky at best.
Iran's geography makes them feel invincible as a ground war would be a real challenge for invading forces. Air and drone attacks would have only so much effect...air power can't take or hold ground and that's what is needed to quell Iranian progression....
Nobody wants to make that call for obvious reasons....
You were in the military, not sure if you spent time in the Middle East?
In my career, I had a rather big portion of the Middle East in my portfolio and was physically based there for 5 years as a portion of my assignment.
Where I totally disagree with you is resolving matters by diplomacy.
The Middle East has no concept of the principles of democracy, they do not understand diplomacy.
They understand and respect authority, and they act by fear of the results when they disrespect authority. Even the Islam religion is based on those principles. They also have very strong tribal bonds.
I employed, coached and developed a few senior managers, born in the Arab world but college educated in the US. One would think that background would change their beliefs to a democratic Western culture, but in most cases it is impossible.
Even today, I respect who they are, how they think and I do not judge their different values to my culture, of which resolving matters by diplomacy is the accepted protocol.
The Western World would condemn the murder of Kashoggi. While I certainly don’t approve of it, I understand why it happened, that it is part of an authoritarian culture and those values have been entrenched for centuries.
For us Westerners having a dream of installing democracy and diplomacy in the Middle East is about as naive as it gets.