Whether the USSR would have actually intervened is irrelevant....the mere tail risk that they might was enough to scare the hell out of Washington. The US had spent decades at that point meticulously avoiding a direct conflict with the USSR in theatres across the globe, and they weren't going to gamble on starting World War III on the Soviet border over a bunch of clerics running around in Tehran . That uncertainty alone gave the Islamic revolution a cold war deterrent shield in those early days. The US sat on its hands paralyzed by fear - not because they we're certain the USSR would intervene but because they couldn't be certain the USSR wouldn't! The Iranian regime exploited this Cold War anxiety to its maximum effect.
You missed the second part of my explanation re: hostage crisis - yes expelling diplomats removes a foreign threat, but the hostage taking was doing double duty for the Islamic revolution. By manufacturing a 444-day national emergency, Khomeini forced Bazargan’s moderates to resign, purged all his secular rivals, and locked in absolute clerical control for the Islamic revolution. In that period every domestic rival was labelled an American agent seeking to destroy the Islamic revolution. See it wasn't just a counter revolutionary security operation- it was a manufactured crisis to allow for a highly calculated internal power grab. It allowed Khomeini to brutally consolidate power - highly rational for that narrow purpose.
The realist answer here is quite simple - structural and geographic considerations drive who becomes enemies over time.......as you pointed out yourself Iran and Israel had a relatively cooperative relationship pre-1979. What changed outside the obvious? The structure of the Middle East. Think of it like a mini-version middle power version of the famous thucydides trap.
When shared Arab enemies collapsed in the region, Iran and Israel were the only major powers left - a duopoly of power & influence, this made a structural rivalry inevitable as both pushed to grow its relative power in the region(Germany - France etc.). As for the US, I mean Iran didn't arbitrarily pick an enemy here....due to the 1953 U.S.-backed coup, Washington was already an established existential threat to any regime that took office in Tehran that wasn't to Washington's liking. But "who started it" is nonsense best left for kids in the playground...structural realities are what sustain conflicts over time.....the Israeli-Iran regional security competition would have inevitably pulled in D.C. over time regardless of the hostage incident to say nothing of the Cold War dynamics sitting above that.
I will concede one thing however in the neighbourhood of your point above about creating unnecessary enemies - in a perfect world if Khomeini had an alternative vehicle to consolidate power domestically in 1979 to the US hostage crisis he should have taken it.....I don't know enough about the options available to him at the time to judge rationality or not but the hostage crisis did indeed move Iran from being enemy number 52 on the US's enemies list to being much much higher (to put it mildly).
I think in this area one can argue that perhaps Khomeini/the regime miscalculated the ROI of the hostage crisis which is not the same as being irrational nutjobs.
The moderator - mediator here is clearly capability. You've seen the threat equation before -
Threat = Intent x Capability
Death to America is rhetorical nonsense coming from the mouths of any Iranian who spews it - what US person goes to bed at night concerned that Iran may do something that would threaten the US's continued existence, the answer is precisely zero US persons. Look at the asymmetry in capability here. Death to Israel carries more freight as Iran is a larger country in closer proximity and as we've talked about engaged in a regional security competition with proxies to boot....but again let's be real here, Israel has the US security umbrella, vastly superior military capability, larger economy and if that weren't enough a nuclear capability. These phrases are hot air and rhetorical nonsense because simply they are not underpinned by any credible capability to carry them out. Iran is a threat to Israeli safety and security but it does not rise to the level of an existential threat to Israel.
And as regards US and Israel wiping out Iran......lets be serious here, the reason they haven't is because invading and occupying a massive, mountainous nation of 90 million people would require a catastrophic expenditure of blood, treasure, and political capital. The ROI on total annihilation is deeply negative. Therefore, the US and Israel make the highly rational, calculated choice to manage the threat through crippling sanctions, cyber warfare, and systematically degrading Iran's proxy networks....containing the problem without paying the suicidal cost of a full-scale ground war.
Epic Fury has proved both my points above again.....nobody anywhere considers the Iranian threat serious enough to expend the massive cost required to annihilate the regime. The reason Israeli/US neo-cons can't rally popular support for further military action in Iran (boots on the ground) is for that precise reason. Put simply Iran is just not a credible of enough threat that it is politically popular enough in the US to bother to pay the high price required to annihilate them.
'First shot' arguments are just nonsense and I wont get dragged into one except to say that Iran would say the first shot was the US's in 1953 with the coup they orchestrated against the regime in Tehran....but as I said before "who started it" arguments are best left to kids in the playground. Structural contemporaneous realities are what sustain conflicts over time not who did what back in the past or when it comes to the Middle East who did what back in 500 BC or 20 AD and all that nonsense!!!!!
re: Attacks by Hezbollah & Hamas.....my language wasn't precise enough here previosuly but goes back to offense-defense indistinguishability arena. Yes its offensive in nature but its fundamentally a defensive strategy... the aim for Tehran, is to impose continuous friction on Tel Aviv that sits in a geopolitical grey zone. It ensures Israel must perpetually expend capital just to manage its near backyard.....a rival expending military capital near-shore has by extension less military capital to expend offshore i.e. in proximity to Iran. Again a form of offense that is functionally defensive. It is a deterrent in the sense that it shifts the theatre of the conflict to Israel's backyard and away from Tehran.
Of course the other point re: Hamas and Hezbollah that nobody likes to acknowledge but is true - is that Iran has a principal-agent problem with these groups......they exert great influence over them no doubt but they don't perfectly control them and their interests aren't perfectly aligned.....US intelligence post Oct 7th shows that Tehran was as shocked as anyone regarding what Hamas had done....indeed many commentators have indicated that if the leadership in Tehran had been aware of Hamas's plans re: Oct 7th they would have attempted to stop it for the very reasons you point out....it was an act of such brutality that it invited the dog AND the owner to be shot. Iran wants low level friction that continually consumes IDF resources & political attention in Tel Aviv but not so high that attention turns directly to Tehran.
Nothing in proxy warfare management is perfect. Your local proxy pitbull designed to impose continuous low level friction on your rival and keep things in a gray zone...... is an animal you only partially control and because their risk calculus is not your your risk calculus things can go wrong.....to your point and I agree with it.....Iran has a tail risk here via this proxy network that could go badly wrong for it SOMEDAY....but let's be clear, the owner hasn't been killed yet after 45y years of imposing that brutal proxy friction. Highly brutal, highly rational.
The U.S. and Israel have spent decades and billions "shooting the dogs" in Lebanon, Gaza, and Iraq, but they painstakingly avoid invading Iranian soil. Even now Epic Fury was just an aerial bombing campaign that can't gain the momentum to move to a ground invasion. Hell the US couldn't even sustain the blockade of the blockade after the bombing stopped! Why? Again because even the ROI on the blockade of the blockade was negative - never a mind a direct ground war with a mountainous nation of 90 million people which would be catastrophically negative relative to existential risk Iran poses to the US. For Israel we can argue something else but that circles back to the capability problem Israel has....it can't annihilate Iran on its own.
In a perfect world the leadership in Tehran should be disappeared but the world isn't perfect - they've entrenched themselves in power there with the distributed control system the purposely designed to be regime change proof. The SOH saga proves how little it takes to shut the Straits - and the world needs some kind of central Government in Tehran controlling its vast territory (if only to keep the oil and fertilizer flowing). Turning Iran into Syria for this reason alone is not a good idea.
The dilemma remains the above for Bibi/ the US etc......the Iranian threat (intent x capability) has never risen to a level where the ROI makes sense for the US/European allies to greenlight the massive investment required to take out the regime (despite Bibi's years of threat inflation) and Israel alone hasn't the capability itself.......I would love to see them gone tomorrow but it's clear the cost (relative to the actual threat level from Iran) does not meet the threshold that makes sense...I totally get it, try saying the above to the family of the victims from Oct 7th or those living under air raid sirens in Northern Israel caused by rockets coming in nightly from Hezbollah.
The reality however of Epic Fury ending in an MOU has proven that devastating algebra once again.....Iran and how it chooses to execute its foreign policy is a blight on the world and the Middle East but it calibrates its chaos so the juice is never quite worth the squeeze in terms of removing the regime. The one nation for which the algebra works and it would be 'worth it' (Israel) hasn't the capability to do it alone.