The cost of doing nothing is going to be large.

Apart from the oil, there is the fertiliser that isn't being shipped. That means that august crops are going to be down. Assuming its a good year. prices go up, which means we can expect a wave of overthrown governments (similar to the arab spring) in 12-24 months time.

For the USA that means inflation, along with a credit crunch (probably)

Given you compare the cost of a US operation to open the straits to the Vietnam War, it seems prudent to mention that the outcome of the Vietnam war, according to Wikipedia, was a North Vietnam victory.

> I don't see any compelling evidence that the US couldn't open the straits if it really wanted to, it's just that the cost in lives and hardware would be unlike anything the US has seen since Vietnam, maybe even the second world war

The US invaded Iraq and toppled its government; Iraqi militias are still firing drones and missiles at US bases. Tankers and oil infra are much softer targets… all it takes is hitting one or two tankers and folks will stop shipping.

> I don't see any compelling evidence that the US couldn't open the straits if it really wanted to, it's just that the cost in lives and hardware would be unlike anything the US has seen since Vietnam, maybe even the second world war.

The second half of that sentence is literally explaining why the "impossible" you reject in the first part.

The US wasn't doing nothing about Iran though. The JCPOA was a thing, before trump tore it up. This approach is about the dumbest way Iran could be handled, which makes sense given who is giving the orders.