I imagine part of the reason they shot it down is because the rhetoric coming from Washington is such, that an attack could come at any moment and is hard for the Iranians to tell if this is it or not, (which I think is part of the U.S. tactic to provoke them to do something stupid).
The U.S. would not tolerate Chinese drones off its coast either.
Now, China is competitor number 1, so I don't think they would, (unless China agreed to do the same at its borders). And is not like Iran is not tolerating countless U.S. military bases around its borders, I just suspect they're at the edge of their seats, expecting an attack and sending an armed drone to their border doesn't seem too friendly.
The U.S. also knows that Russian planes flying are not there to bomb them, whereas the Iranians are hearing constant rhetoric that the U.S. is just about to bomb them.
Moreover, as I said, the U.S. knows Russia is not about to conduct a surprise bombing raid on them, so does Russia know the same of the U.S. - They both have nuclear weapons and doing so would be catastrophic for both sides. Iran on the other hand expects a U.S. bombing raid any moment and in fact Trump just admitted one was ready to go ahead, so it's a bit different.
In fact, I suspect the U.S. knows all this and provoking a reaction from the Iranians to support further action from the U.S. was precisely the goal of this drone.
As to motives, who knows. Iran could be trying to move confrontation from economic to military, where it has a shot on regional parity. With all talk about Bolton, Iraq, Vietnam and on this admin is very docile. Iran came out on top from this confrontation, bolstering its regional influence, so why not.
I am not too sure. The US are already attacking Iran, by strangling its economy, effectivly subjecting it to a blockade. They don't need an open war for that, it would be an unnecessary cost, economic and diplomatic- but at the same time they have to show they're absolutely ready for it.
For the US (but in fact Israel and Saudi Arabia, the only ones that gain from this) the best option is to keep choking Iran in silence, without much hassle, so the rest of the world can keep looking the other way.
That is true, it's a policy the U.S. has employed in Iraq prior to the 2003 invasion and is now also perusing in Venezuela. In some ways you're right, it makes it look like Iran's acting in a vacuum and the U.S. is doing nothing to provoke it.
On the other hand, if they were to bomb Iran, it's not like they'd let the sanctions go in exchange for the bombing, it would be in addition to the sanctions. And yes, it would draw minimal condemnation from the EU, China and Russia, but that's about it.
> Iran is not inclined to help Trump come down from the tree he has climbed and would rather keep him confused and cornered. Furthermore, Iran would love to see Trump fail to win a second term, and will do everything to help oust him from the White House at the end of his mandate in 2020.
> Moreover, Iran has established a joint operations room to inform all its allies in Lebanon, Syria, Iraq, Yemen and Afghanistan of every step it is adopting in confronting the US in case of all-out war in the Middle East. Iran’s allies have increased their level of readiness and alert to the highest level; they will participate in the war from the moment it begins if necessary. According to sources, Iran’s allies will not hesitate to open fire against an already agreed on bank of objectives in a perfectly organised, orchestrated, synchronised and graduated response, anticipating a war that may last many months.
> Sources confirmed that, in case of war, Iran aims to stop the flow of oil from the Middle East completely, not by targeting tankers but by hitting the sources of oil in every single Middle Eastern country, whether these countries are considered allies or enemies. The objective will be to cease all oil exports from the Middle East to the rest of the world.